In the fiber arts, I would have to say that the best general good-for-you actifity isn't knitting. It's spinning. I was working with the carbon fiber yesterday and really paying attention to what I was doing, and if you get an easy-to-work-with fiber (like merino wool or S American mystery sheep from Colonial Wools) and spin a reasonable weight like worsted or DK, it is probably the best of the fiber arts for physical therapy. It uses both hands, but gently. (At least until you spin for like eight hours straight, and I'm pretty sure NOTHING is good for you at eight-hour stretches, except maybe sleep.) The act of pre-drafting the fiber, of smoothing it out, and holding it in your hand, is both soothing and reasonably easy. I've improved my grip and pinch strength, with little or no bad side effects, even after marathon eight-hour sessions that I knew better than to do. I poked around in the archives for some photos of my hands, spinning, and here are a few to give you an idea. In most of those photos my right hand is taking the photo, but usually it is used to either support the roving or mirror what the left hand is doing.
It's easy on the hands compared to knitting, where there's a good bit of stress on the knuckles to pull the yarn where you need it. (These things are, of course, relative.)
Knitting is, of course, good physical therapy and helps the strength and motion. Some things are harder to do than others. Some of that depends on you, specifically, and what you've got problems with. I find that fine gauge is easier on the hands because there's less weight, but it requires more fine-motor skill to accomplish. Wool and other animal fibers are generally easier to knit with than plant fibers (and less obviously, woolen-spun yarns are easier to knit than worsted-spun, but I doubt most people would even notice). The object in knitting is to make something that doesn't unravel. So however you get the yarn around the needle, is the right way. Though for normal hands, Continental (yarn in the left hand, 'work' done with the right hand needle) is easier on the hands. If your hands aren't normal, do whatever works. Again, there's no wrong way.
Sewing - hand sewing - though I mostly hate it, is really good for fine motor skills, and again is relatively easy on the hands. Mind you, you can make it insensible by sewing four layers of denim, or quilting through umpteen fabric layers, or whatever. One reason I like my antique-style ribbon work is I usually don't sew through many layers, and the weight of the ribbons isn't much, so it's easy to haul around. I do know a quilter who had to quit after half a lifetime of twelve hour days of hand-quilting for pay. Again, the body isn't meant to do ANYTHING for twelve hours straight.
Remember, if it starts to hurt, you need to knock it off. Usually a fifteen minute break is enough, but if you're still hurting at the end of your fifteen minute break, listen to your hands. TAKING PAINKILLERS AND THEN GOING BACK TO THE ACTIVITY THAT MADE YOU HURT IS DUMBASS. (Yeah, I do it, but for me it's the chronic pain thing. And even so, I get sent out to a specialist every couple years to make sure I'm not ignoring something important. Even then it's kind of dumbass.) Options for the ol' hands include heat, ice, anti-inflammatories (Tyelenol or whatever), massage (a good hand massage is as good as chocolate), TAKING A BREAK, simple exercises, and plain old doing something else. One way I manage to knit for days at a time is, I'm really not. I play my strategy games. So I knit for a minute, game for a minute, knit for a minute... It's a bunch of short breaks and I manage to get a lot more knitting done that way than if I were to sit down and JUST KNIT. Though of course it does take longer.
Something else most of us do, that I feel compelled to mention in the hand category: cooking and the kitchen. You can have major problems in the kitchen, especially when you add in nerve damage and trouble hanging on to things. Some thoughts:
-It's actually good for your hands to do dishes. The nice warm water increases the circulation and the wide range of non-repeated motions are good exercise. (I hate it, but it's true. Sorry.) If you drop a dish, do NOT try to catch it. You'll wind up either cut, or otherwise smashed. Better to break the plate than slice yourself. Really.
-Keep your knives sharp - you need less effort to use a sharp knife - and learn knife skills. "Knife Skills" is the collective term for all that textbook stuff used in restaurants to cut stuff up. They've got specific methods for chopping and slicing and scoring and blah blah blah. I learned them while working at a restaurant (as the bookkeeper) during my second orthopedic surgery. The chef saw I had hand problems, knew I liked to cook, and immediately said 'You need to learn knife skills.' I thought he was just looking for cheap labor, but you know what? Since I learned, I can't think of the last time I cut myself. And before that? When my hands were GOOD? I cut myself all the time. There's a reason restaurants use these methods; they're efficient. Having the help cut themselves up isn't efficient.
Alton Brown has an entire episode of Good Eats about knife skills... I'm betting it's available on a lot of the gray-area download sites. Wait. Found him on YouTube. Part One, and Part Two. Even if you can't get your fingers to do all the things his do, you can get the idea and even applying HALF the stuff makes you safer. I strongly suggest using the 'new school' onion dicing method. (Anyone got an idea how I can tactfully teach this stuff to my mother-in-law who traditionally winds up with stitches every year or two at the holidays? And bleeds at almost every big dinner she cooks?) Oh, and bottom line? Get a good knife. At least one.
Honestly, I think everyone's better off with knife skills. The husbeast has picked them up from me, and from watching Good Eats with me. The last time he volunteered at a charity cookout he was showing everyone else how to cut things up properly. Everyone was vastly impressed. (Plus it went faster and no one bled.)
Otherwise, if you have a bias against kitchen gadgets, get over it. I do; I'm one of those maniacs who used to juice a lemon with a fork. I blame "Great Chefs of the World", an old PBS series where they did just what it says: went into great restaurants and showed famous chefs preparing the dishes they were famous for. And these chefs were making amazing gourmet, world-famous, got-them-on-TV food with one beat-up pan, a dinner fork, and a chef's knife. I still fall back on that attitude. But you know what? With my hand problems, I need to get over it. For example. I think egg separators (doohickies of several designs that separate yolks from whites) are the silliest things in the world because you can use your hands/fingers to separate eggs perfectly well. But cold egg hitting my fingers feels like someone hit my knuckles with a hammer. I need to get over it and buy the damn gadget. (Preferably before I dig into the holiday baking.) You certainly don't need EVERY gadget on the market (who could afford them all?) but if there is a gadget for a certain thing you do a lot, that bothers your hands, buy it already.
Otherwise, stick with the obvious: If it hurts, don't do it. Ongoing physical therapy shouldn't hurt, or not much. The original get-it-working is brutal, but keep-it-working should be fairly painless or you're doing it wrong.
Anyone interested in video of my range-of-motion exercises I had drilled into me during three months of hard time in the physical therapy department?