Why? Isn't that technology from the 80's? Why would I need to use a P/S2 device these days?
To use my IBM Model M keyboard, of course!
If you've never used one of these, you're missing out. (unless you can't touch-type, but that's another problem...)
There are all kinds of sites that rave about the benefits of the Model M, so I won't go into too much detail. To summarize, the tactile feedback is great, you know for sure if you've hit a key or not. Also, the thing is built like a tank--if mine were a human, it'd be old enough to drink.
I got mine from MSU salvage. That's right, they were just going to throw it out. I think I paid about five or ten dollars for it. It was filthy, and the right ALT key didn't work. After a few keyboard wipes, it looks brand-new. I didn't use the ALT key anyway, so that didn't bother me. A few years later I got a replacement spring... that's right, the only reason it wasn't working is that someone lost the spring under the key. I put it back in, and it's as good as new.
Mostly, though, I love it for how it types. Your fingers don't get as tired, you can feel when a key is pressed... it's great. The junky USB keyboard I've been using in the meantime feels mushy. Sometimes a key will press when I didn't think I'd hit it that hard, other times it'd double-key when I pressed too hard... yuck. In its defense, it was very cheap, but the Model M is two to three times as old, and has none of these problems. Many people have reported increased typing speeds on the Model M, and I believe it.
Also, no Windows keys! I can't stand them. I'm always hitting them on accident.
If you write (well, type) for a living, you've got to try one of these out. I can't really do it justice in words, you've got to try one. You can get them from a variety of places online for cheap, or brand-new from Unicomp.
Brand-new Model M's: http://unicomp.com/
More info on the IBM Model M, as well as a few old ones to buy: http://www.clickykeyboards.com/