I've noticed that tenkeyless mechanical keyboards are a huge fad on 4chan's /g/ board. From what I can tell, the tenkeyless layout is more ergonomic since it allows you to center the keyboard more with your body. I'd almost consider getting one since I like the idea of that, as well as the possible desk space savings, except that I'm extremely accustomed to having a numeric keypad, and I find keyboards lacking them to be annoying to use.
One thing I've seen people with TKL keyboards do, is that they'll get an accessory keypad and put it on the left-hand side. It seems like it defeats the purpose of having a narrower keyboard, as it would take up the same amount of desk space, but thinking about it now, it would still allow the letter keys to be more centered for more ergonomic typing. I think using a numeric keypad on the left side would be awkward to get used to, but it would be doable.
I wonder if anyone makes cheaper rubber-dome TKL keyboards, because I'd like to try one out just to get a feel for the layout, but I don't feel like forking out for a mechanical one.