Not necessarily good on battery life. A lot of people are complaining that after updating to iOS 4, their battery life on the 3G and 3GS went down considerably. And there are those that are still using the 3GS that are still having battery life issues as well as the random reboot on calls issue (bunch of posts regarding this on the Apple Discussion forum, about 200 pages worth...each thread). Many have been able to fix this when they finally got forced into upgrading to the iP4 with 4.1 (me being one of them). But now there are those people who have an iP4 that updated to 4.2.1, and are experiencing those issues, and 4.3 hasn't fixed them. From what I hear too, people with iP4s who updated to 4.3 are also having issues with deleted stored texts. That when they send a text, all their stored texts were suddenly deleted. As well as the short alert tones and vibrate not working as they should when receiving text messages. Some have their notification set to 10x, but will only alert the one intial time. And with half of the new text tones being dwindled down to a fraction of their length from the previous 4.2.1, if you miss that tone or the one vibrate, you won't know you got a message until you actually look at your phone again.
Maybe this is Apple's way of getting everyone with a 3GS or iP4 to upgrade to the iP5? Worked previously with 3G and 3GS users. lol