I used to bump charge last summer. I quickly learned to charge the phone with the power off. I wish it wasn't the case, as I used to leave my blackberry on 24/7 and used quickpull automatically to reset the device overnight. My cell phone is my main phone, so turning it off I could miss an emergency call in the middle of the night, but by turning it off it will fully charge the battery.
Bump charging will do the same thing, but shorten the battery life in the long run as a battery only has so many charging cycles before it dies. Doesn't matter if you charge 90% or 5% on a cycle, your still using a cycle. I'm sure even with bump charging the battery will last at least till your next upgrade, but I'm hoping to keep this phone till it is obsolete. I'm tired of paying $200 every 20 months when the phone I have is just fine.