I know there are folks that disagree with me (and that's okay!

), but I believe the battery stops charging when its full and does not charge any more, even though its on the charger. Here's my example: you put the phone on the charger when you go to bed, it completes charging in a couple hours. It is then on "stand-by", not using much juice (depending upon what you have running in the background) until you un-plug it and start to use it. So, since it hasn't been charging for 3-4 hours, almost immediately it drops to it's correct charged level. Plug it back in and it will start charging again until full.
One of the threads suggest a long dance in which you turn off and plug in and turn on and plug in, but you're essentially doing the same thing. When you unplug, or restart your phone, it re-checks the charge and charges as necessary until full. I believe this is a measure by which the phone and battery are protected from over-charging. The Samsung Omnia does the same thing.
Best practice for me: charge it up over night. Then when I get up in the morning, I unplug it, check my email and whatever, then plug it back in while I get ready for work. Out the door with a true fullycharged battery.
As always, ymmv.