To summarize: a charge cycle is defined as draining the battery and charging it back up - not simply plugging in to top off when you get home from work. According to Snell, charing your iPhone's battery up 25% is equivalent of spending 25% of a charge cycle - not the entire cycle. Further, after 400 charge cycles the battery is in absolutely no way dead or useless, nor is it in need of a warranty replacement or support from AppleCare. After those 400 cycles the battery's total capacity simply drops to about 80%, just like an iPod and many other lithium-based batteries. In other words: unless you're completely draining your battery every day and charging it back up completely every night, you shouldn't have anything to worry about for the life of your iPhone.
While it may still be a bummer for some ultra-mobile users that the iPhone's battery isn't user-replaceable on the fly, it should still offer plenty of juice for the typical user's habits for many years to come.
[via Daring Fireball]