Bump Charging definitely "tops" of the battery in my experience, despite what others claim on XDA. Using the MIUI Rom (with Launcher Pro), when charging with the phone on, you can see the percentage on the lock screen as it charges. When the light turns green, the percentage on the lock screen only reads 93%. I found this quite interesting because prior to using MIUI the phone would say 100% charged while on when charging, but within minutes of being unplugged, it would drop to 93%.
When charging the phone with the power off, it charges to the full 100%. It can definitely give you an hour more battery throughout the day. By bump charging (turning it off after green and topping it off) you are essentially running your battery through 2 charging cycles. Its only bad in that it will shorten the life of the battery. A l-ion battery only has so many charging cycles. Wether the battery is at 50%,90%, or 10%, it uses a charging cycle when plugged in.