I have both an iPhone and a BlackBerry. They are not in the same universe as far as battery life goes. On a good day, the iPhone battery last maybe 6-8 hours. In other words, I can take it off the charger when I leave for work and it still have some life when I leave. On a bad day(a), the BB is good for 24-36 hours. They are not comparable. Not even a little. Now, that doesn't mean I don't love the iPhone, but the battery life simply sucks. That's just the reality.
Depends what you do. I have a corporate BB, and it'll run for days on one charge. But all it's doing is receiving data in bursts, with me sending the odd reply. My iPhone is used for phone calls, texting, email, internet, checking the weather, games, following the Astros, listening to music, posting on Facebook, IMing, keeping my calendar, Google maps, taking notes, using the calculator, searching for music with Shazam, taking and viewing photos...
Shortly after I first got the iPhone, I went on a trip to NYC. Left the house at about 6am with a full charge. Listened to music on the way to the airport and made a couple of calls via Bluetooth. Made a couple more calls at the airport in between more music, and sent some emails. Boarded the plane and (after takeoff) watched a movie on the iPhone. More calls, emails and music at the other end, before heading to my first meeting. Continued the emails during the day. Used Google Maps to get from appointment to appointment. Occasional calls. Met some folks for dinner, but when walking to the restaurant, noticed that there was a massive plume of steam erupting from Lexington Avenue. Used the 'net to find out it was a burst pipe and not al Queda. Took some photos and emailed them to people. Had dinner and drinks and more drinks. Got back to the hotel after midnight (after a trip to the 24/7 Apple Store where I saw Robin Williams). iPhone still hadn't hit the 20% red line.