While thoroughly violating the USB spec, I've started powering my B3 from  
my PC's USB port (nominally 5V, IIRC, the USB standard permits 4.5-5.5V).
The red Reset light glows dimly when I do this, since the LED's pulled up  
to VRaw, rather than 3V, but the board works just fine.
The schematic states 4.6Vmax on VRaw (which turns into VBatt). I can't  
remember why, for the life of me. The MAX1586 (Xscale power) claims to be  
OK up to 5.5V, and the TPS75003 (FPGA power)is good to 6.5V. Is this a  
hangover from an earlier design iteration, or a real limit? (being able to  
be USB powered has a certain simple charm - I'm now running with a 1N4001  
in series with the PSU, to stop the red glow and reduce the damage a  
backwards-power blunder would cause...

Steve