SAdelman-I'm experiencing symptoms somewhat like yours..usb-everything's good. Wall charger(s) would charge everytime if phone was powered off. Phone on however, would not charge.
I purchased a cradle off ebay that came w/o charger-just cradle. Plugged one of the wall chargers I'd been experimenting with into the cradle, cradled the phone (turned on) viola! charges like a champ.
It's been a week or so, charging each night and all's been well...'till this morning. Took it off the cradle this am, message comes up saying Main battery is critically low, and needs a charge so's not to potentially lose some data. Damn. Put it back on for 15 minutes, and it had taken some charge, enough that the message didn't come up. As I type, it's plugged into the usb cable and charging.
I even purchased and installed Fizz monitor so I could see the word "charging" when it was plugged into a/c power. I'm sure it said it was charging last night, but I could be wrong...staff golf tourney yesterday w/ quite a few beers involved.
Probably doesn't help you much, but at least you know you're not alone! I don't want to blame the phone so much, as everything works perfectly with the usb cable.