I've had the 7100g for a little over a week- I'm on my third batter drain cycle. Screen is at 60, which is very readable, even with a screen protector on it.
IMO Bluetooth seems to be the biggest battery drain (definitely was on my 7290) with web use and phone right behind it, with email using the least (at 60 screen). My 7280 would last for a week, my 7290 for about 3-4 days and it seems the 7100g is no more than 2 days, so you be the judge of whether the battery life is an impediment to buying. For me, the 7100g is a better phone than any of the 72xx devices, hands down. No comparison and I didn't think I would use the speakerphone as much as I do, but it is a useful feature and people on the other end tell me the quality is great.
I'm on cingular in NYC and the coverage is better than it has ever been in the past, and improving, although it is expensive as compared to t-mobile (I wouldn't recommend it in NYC- everyone I know who uses it for voice and/or data complains about it). I used to have AT&T a few years ago and went to Verizon for a few years when I was just using voice. Cingular is not currently rock solid like Verizon is on voice, but it definitely seems that it is improving over the last 6 months, and it's totally adequate for my needs. By the end of 2005 when all the towers from AT&T wireless are supposed to be contributing to a single 'Cingular' network, I think it will be as good as Verizon in NYC, and much better outside of the city.
Also, If you plan on 'pocketing' the 7100g, get a screen protector. It fits in the front pocket of my jeans. I'm using a holster, but I can see how this thing can get dinged and scratched more easily than the 72x series. Go to www.screenguardz.com
or search for screen protector in this forum and you should be able to find a list of vendors...