A few thoughts on the 8830 relative to the Cingular 8800.
1) The OS on the 8830 includes some of the features that I first read about on the Curve--e.g., spell checking and folder-creation. Very nice.
2) The trackball doesn't seem to be as responsive as on the Cingular 8800. Probably just normal variation.
3) Browsing the Internet appears faster than the Cingular 8800. Full bar EVDO vs. full bar EDGE loaded
Google about 3 seconds faster on the 8830.
4) The speaker on the 8830 is definitely softer. Not too soft, though--on the 8800, ringtones, etc. were comfortable at low and intolerably intrusive at high; on the 8830, they're comfortable at medium and tolerable at high.
5) I prefer the Cingular default theme/layout to any of the layouts on the 8830. That said, with the ability to manipulate folders and move icons around, I can pretty much do whatever I'd like on the 8830. I'm using a "personalized" version of Dimension Icon.
6) Screen, build quality, etc. all seem the same.
Now open to questions, which I will try to answer to the best of my ability.