We've been having a look at possible new designs for our library website and today we've been running usability testing on two favourites. What we do is have the tester in one room with a facilitator beside them, a note-taker behind them, and next door a group of observers watching a) a view of the computer screen and b) a closed-circuit video of the tester. (The note-taker is in the room in case the video link breaks. Testers are told other observers are watching but that we're not recording.)
Normally for the closed-circuit link we use video equipment booked and carted over from the AV department, but today when I arrived to do my duty as an observer I discovered they'd set it up using Skype instead. It worked well: there were problems with sound volume (a function of the hardware: we used our regular webcam, but a clip-on microphone for the tester would probably be better), but quality otherwise was just fine.
(The usability testing was, as usual, fascinating. Although it covered the library website as a whole, there were several points where testers were using the library catalogue (of which, I was recently part of a project group to find and fix as many things as we could fix for free in a short timeframe), and one question asked was if they'd noticed any of the multitudinous changes. Yes: they noticed the new colour scheme. On the plus side, they approve.)