speed. the processor running the java o/s on the 7290 is a lot slower than the 8700. I believe we're taking about 50Mhz vs 312Mhz. so the 7290 is noticably less snappy after using a 8700. Oh, and the screen. After using the gorgeous 8700 the 7290, is well, ick. The keyboards are different. some say the 7290 is better. Well the keys feel a little bigger and farther apart on the 7290. But after using both, I think I like the 8700 better by a little bit. But I have thinner fingers. I can comfortably type on either. I use the 7290 everyday.
I don't like webbrowsing on the 7290. You're limited to GPRS speeds (similar to 56k dialup) compared with the EDGE speeds (Similar to ISDN, or slower broadband). Pages seem to take between 3-7 sec to load. I don't like it.
The 7290 is dead reliable. The keyboard is nice. It's just a slower unit all around (but still peppy enough to be very usable).