Not really my first day with the iPhone, but certainly the first day I can use it for the whole day. I’ve had it going since about 6am and got a 20% battery warning at around 12:40. All in all not a bad run.
I’ve had wifi and bluetooth on, email auto-checking every 15 minutes and used the web extensively. I’ve only made one call and that lasted about 15 minutes.
In my previous usage with WiFi enabled handsets, this is by far the best.