I was curious how much power the 900 series Roombas could provide through their USB ports since these models don't have direct connections to the battery like older models with the mini-DIN connectors. Furthermore, I wanted to be sure I wouldn't damage anything if I did something stupid while connected to the USB port.
I disassembled a 960 to examine and make this schematic. The whole interface appears to be sufficiently protected from both over-current and over-voltage events. The Zener and fuse values are best guesses based on datasheets I found online, but these parts are so small they don't have any manufacturer's identifying marks.
To summarize, for future reference, the 900 series Roombas should be able to safely provide up to 500mA through their USB ports. This shouldn't surprise anyone since the USB 1.x/2.0 specs call for 500mA, but now we have confirmation.