I've been experimenting with xbees and have been powering them from the 3.3V pin of arduino's. I just realized that the 3.3V pin can only deliver 50 ma. (I had stupidly assumed it had capabilities similar to the 5V pin.)
The arduino's seem to be functioning fine along with the xbee radios so if I've broken anything, it isn't apparent.
I doubt it, lower the voltage lower the current draw.
At the worst, the xbee will draw too much, the 3.3V regulator will get warm, the power will sag, you'll lose comm's.
More likely - you have 4.2 to 5V on Tx out to the Xbee, possibly causing damage to Xbee inputs that are expecting inputs no greater than VCC + 0.5V = 3.8V.
May take longer term to become apparent, on either the Arduino or the Xbee.