I routinely plug my Android phone into two different computers.
It is a 3.7v 1500mAh 5.5watt battery. I also have been charging my 808 3.7v batts on USB ports.
Come to think of it, I have been using a multitude of USB powered (no AC) hard drives and audio interfaces on USB ports for years with no problem.
I think that the key to peace of mind on this may be the understanding of AMPS. (Which I dont understand 100%)
Also the amount that you trust the equipment that you are plugging into the computer is designed well.
As for me and my PV devices, I have been plugging into the computer for any
batteries, but not the passthrough. I have a AC to USB (5v 1amp) adapter, and plug the passthrough into that. I am not convinced that I really need to.
The chargers, cartos, attys, and a PCC that I have bought so far have been of very questionable quality and are extremely inconsistent.
I think that the PV industry has quite a bit of room for growth in the quality manufacturing / control dept... I digress, but think it is relevant.
Best, Jake