A few days ago I was cycling to work when a white sedan accelerated across the road and ploughed into me and my bike before driving off. I was quite lucky: I ended up with just a broken right wrist and some grazes. Still, losing my dominant hand sucks. Here's how I've tried to make up for it.
I wrote half this article by voice, using Dragon Naturally Speaking for Windows. I normally use Macs and Linux exclusively, but the voice software's just not there. Even the Mac product using the same engine is pretty bad: it's missing the correction and editing controls that make using voice productive. As much as I hate it Windows is the only option here.
For navigating webpages, I'm using Chrome with Vimium. This lets me follow links by saying "f" and then spelling the letter combination unique for that link. When it works it's lovely, but sometimes Dragon doesn't seem to send the letter input to the page correctly.
For programming, Tavis Rudd gave an awesome PyCon US demo on using voice to code in Python and LISP. It took him several months to become productive, quite an investment. It's better suited to someone with long term RSI or a more permanent disability than to someone like myself whose problem is more temporary.
The other half of this article I typed with just half a keyboard. Our two hands are basically a mirror copies of one another; with just one bit of additional input we can take advantage of this symmetry and pretend to be using our other hand. This is the principle behind half QWERTY typing.
On OS X I found two ways to do this. MirrorQWERTY uses space as the modifier key: whenever you're holding it down, any other keypress is interpreted as being on the right side of the keyboard. KeyRemap4MacBook can be configured to use caps lock to toggle mirroring, a kind of modal method of typing.
Of the two, I've preferred the caps lock method so far because it conveniently makes tab key operate as backspace in mirror mode. This turned out to be important when you're learning and are making a lot of mistakes. So far it's already faster than hunt and peck, but naturally much slower than my former typing speed.
You probably type one-handed all the time without thinking about it, on your smartphone whilst carrying something in your other hand. Equipped with predictive text, phones in portrait mode can be pretty productive at putting out text. It's a shame about their tiny, tiny displays though.
The MaKey MaKey is tiny power-packed keyboard lab that lets you turn circuits into keypresses. I've been experimenting with basic elbow and foot switches: I clip an anti-static wrist band to the Makey Makey's earth pin, and wire some kitchen foil to one of its input pins. Standing barefoot on the foil causes current to pass through my body and trigger a keypress. This is immensely satisfying!
In practice, this works better at my standing desk than on the couch, and isn't about to replace a full keyboard any time soon. It could accompany a half-QWERTY setup very nicely though. If you were severly impaired, having someone combine some simple triggers with Dasher could even let you input text.
Computers are necessary for modern life. If you too find yourself without use of an arm for some period, you will have options. Don't be shy to do some research and use them.