Just updated my original 8G iPhone to 2.1 and now have the problem with the spacebar, Return Key, and The 123 Key not working properly. When I hit the spacebar, I get the letter directly above the keyboard instead.
I think it has nothing to do with the firmware update. It's a "touchscreen" problem which is a known hardware issue. I was able to replace my first generation Iphone even when it was out of warranty. If you're based in the U.S. this maybe an option for you.