Not sure what you maen by this, but there is no problem at all "overcharging" your battery. LI-ION batteries do not suffer from any memory issues. The only thing i would recommend is giving it a full charge when you first have the charge. 8 hrs or so will top it off initially (for me anyways). You will notice that even after your battery hits 100% the little lightning bolt will still be on for a bit longer. This is actually completing the charge. But in essence, you can charge the phone however you want. Every night if you want or whatever. But i would suggest along with everyone else using the wall charger.
You are right, Lithium-Ion batteryies do not suffer from overcharging but the do suffer from a finite number of allowable charge cycles. The link here How to prolong lithium-based batteries explains the whoe issue really well.
The BlackBerry knows what it has as a battery and will stop charging when the battery is full. Go to Options, Status to see the percentage charge.
I use this Cradel BlackBerry 8100 USB Desktop Cradle with 2nd Battery Slot - Desktop Cradle. I have one at three computers. It charges with a wall charger and the sync cable is also attached. On my master computer the device and computer are set to two way sync. On the other two the device over rides the computer. I have three stock batteries I cycle through in the unit and keep charged in the slot in the cradle. The phone goes in the master cradel overnight. I always carry a spare battery but have never had to change it through the day.
Never underestimate what something is "meant for". You'd be amazed what the engineers consider in designing specs for standards like USB. Go ahead and charge up any way you want. The charge rate is controlled by a processor and will do the best possible. Your use of the BB (including obscure things out of your control) will determine battery life. Indeed, "gold" tabs on the back will last longer than 1,000 inserts of the mini USB plug, but the USB serves multiple purposes.
