First: You need to take this very seriously. "Dull, persistent numbness 24/7"? Get thee to a doctor who will react to this news with action. If nothing else, get referred to a physical therapist.
Don't use pads or braces without medical advice. You can actually injure yourself more by bracing your arms, wrists, or hands against things.
Don't assume your wrists are the problem. I have had occasional wrist pain or numbness for twenty years, most of which turns out to emanate from a nerve pinch in my shoulders. Doing certain shoulder exercises makes the wrists feel great. Again: find a doctor or a PT who will give you specific advice.
Don't think that gadgets and gimmicks are the whole solution. They can be useful -- I swear by my Kinesis Advantage keyboard, I have Ergotron monitor arms to put monitors precisely where they need to be, I have a keyboard drawer with an adjustable arm to adjust height, tilt, and distance and with an attached mouse support that I've tinkered with to get the height correct -- but this is secondary stuff. The real secret for me is exercise, strategically placed pillows and cushions [1] and, of course, rest breaks. Get some software that orders you to take breaks, like Workrave or AntiRSI for the Mac. Try not to learn to ignore the software.
Get into shape. You would be surprised at the extent to which walking and biking will improve the health of your wrists, not to mention the rest of your health.
EDIT: Oh, and codedevine is right: Be very careful using laptops, and don't use one for any length of time. They force you into specific postures which are generally terrible. I get away with using mine for one or two days at a time, but only because I've been diligent with my health.
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[1] For the back, not the wrists. Don't rest your wrists on things!
I recently read a post you made about two years ago where you advocate spending $2K getting set up (http://news.ycombinator.com/item?id=104977). On behalf of everyone you've helped with your responses to these threads, thanks.
Btw, I met you last week at the HN Startup Bootcamp meetup. I remember you vividly because everyone else was like, "Hi, I'm Dan" and you came up and were like, "Hi, I'm mechanical_fish" Ha. I was sitting across from you for a good chunk of it :) Hope your Drupal endeavors are going well.
I still recommend spending the $2k. If you're in this for a lifetime, $2k every decade or so is nothing.
But my experience since that last post has suggested that a lot of ergonomics is about overall health. The guy who advocates moderate weightlifting as the solution is probably on to something. When I'm healthy and well-rested and getting even moderate exercise, I can get away with breaking my own ergonomic rules... by, say, using a laptop for more than fifteen seconds at a time.
You can't actually do nothing but sit and type for 14 hours per day, every day, for the rest of your life. All the better reason to make your keyboard hours count. ;)
Heavy computer users with persistent pain who don't at least try the Advantage are doing themselves a disservice. I wrote an extensive review of the keyboard here: http://jseliger.com/2009/07/20/kinesis-advantage . The OP might also want to try the Evoluent Vertical Mouse, which is another effort at better ergonomics.
At the moment, the top-rated post pooh-poohs purely technological solutions and says the OP should exercise. I think the keyboard/mouse combo should be used in conjunction with exercise, rather than as an either/or.
Don't use pads or braces without medical advice. You can actually injure yourself more by bracing your arms, wrists, or hands against things.
Don't assume your wrists are the problem. I have had occasional wrist pain or numbness for twenty years, most of which turns out to emanate from a nerve pinch in my shoulders. Doing certain shoulder exercises makes the wrists feel great. Again: find a doctor or a PT who will give you specific advice.
Don't think that gadgets and gimmicks are the whole solution. They can be useful -- I swear by my Kinesis Advantage keyboard, I have Ergotron monitor arms to put monitors precisely where they need to be, I have a keyboard drawer with an adjustable arm to adjust height, tilt, and distance and with an attached mouse support that I've tinkered with to get the height correct -- but this is secondary stuff. The real secret for me is exercise, strategically placed pillows and cushions [1] and, of course, rest breaks. Get some software that orders you to take breaks, like Workrave or AntiRSI for the Mac. Try not to learn to ignore the software.
Get into shape. You would be surprised at the extent to which walking and biking will improve the health of your wrists, not to mention the rest of your health.
EDIT: Oh, and codedevine is right: Be very careful using laptops, and don't use one for any length of time. They force you into specific postures which are generally terrible. I get away with using mine for one or two days at a time, but only because I've been diligent with my health.
---
[1] For the back, not the wrists. Don't rest your wrists on things!