Love mine, its a top bit of kit. I knew Apple were onto a winning formula when I saw the quality of the third party apps on Installer.app. I wish I could state the same for the 'quality' of crap on the iTunes store because there are only a handful of decent apps.
The device is brilliant. It's a shame its performance is hugely degraded with the 2.xx firmware. Even my Touch is suffering.
Connection/Coverage: I live in the Middlesex area and even there 3G is pretty much laughable, despite O2's map stating that the entire area has strong coverage. My experiences have been less than good. Half the time web-browsing is hardly fast but bearable.
Build Quality: With a Bodyguardz shield on the front, things have been superb. No damage or scratches so far. Wish that I could say the same for the tacky plastic rear.
Battery Life: Could be better. It seems to be getting better recently though, although that could be me as everyone initially hammers their phone on the Appstore etc for the first few weeks before things slow down. If I go to work on a full battery, I generally am down to around 30% by the end of the day after making a few calls and Twinkling at lunch. Suffice to say I have now got a dock at work for charging.
In general the device is top notch. What does bring it down is Apples stupid 'no background apps' rule. Sorry but that is pretty poor given that none of the decent third party apps hog the cpu and they all do a stellar job. BossPrefs, Customise 2.0, Summerboard, Intelliscreen - all awesome apps for jailbroken phones. Meanwhile the Appstore trundles along with nothing but crap bar a few decent apps including Remote. We need more 'Flashlight' apps plz thx.
Another killer is firmware 2.xx. It is hurting both Touch and iPhone a lot. Wish they'd sort out the issues quick - especially the random one where I end up pressing the Home button about five times before it actually does take me to the home screen.