I'll chime in here as well, as a pretty hardcore computer geek with LOTS of professional experience in both hardware and software. Modern computers have built in protection for current issues on the motherboard. If your computer is reasonably modern (let's just say for the sake of argument under 5 years old, which is FOREVER in hardware terms) and not otherwise damaged the likelihood of this happening is extremely low. The hardware itself has a polyfuse that will overheat and shut itself off temporarily if need be. Software also monitors current draw, and you might have seen posts by others where a popup message tells them something along the lines of 'Your USB accessory is drawing too much current and has been shut down'. As a geek who is overly protective of my equipment, I have no qualms with using them directly plugged in. Now having said that, anything is possible, but I'd wager a fair amount that if it's ever happened, it was the result of something else contributing to the issue.
As with everything though, if it concerns *you*, then by all means, use a wall adaptor, a power pack, or a powered USB hub. There are a lot of options out there, and peace of mind is important!
