I wouldn't expect significant upgrades in the next generation of Ipads. Apple can't stuff EVERYTHING in the second go around, or you'd have no incentive to upgrade to generation 3 when the time comes around. You can 'probably' bet on an upgrade from 256 to 512 ram( why they didn't do this the first time I'll never know, probably goes back to my 'keep em coming back for more' theory), and cameras. You have to decide if those features are worth it to you.
The nice thing about Apple products, is that they have great resell potential. There are people I know selling their 3rd gen ipod touches for a decent amount of money to upgrade to 4th gen. I doubt you'd have much trouble selling the current pad down the line, if you feel the pressing urge to upgrade the next time around. In the meantime I'd go ahead and buy with confidence, and worry about enjoying the pad to the fullest today, and let tomorrow take care of itself. It is, afterall, promised to no-one...