I'm currently using AO to supplement my review books and stuff, and am finding it pretty helpful. Just want to add that they're very good to listen to while commuting or even just the 10-15 minute walk to class (they're divided up into very short tracks, usually around 3 minutes long). Originally, though, I thought I'd be able to use them while doing relatively mindless tasks (entering data in the lab where I work, for example), but it turns out that I need more or less my full concentration to listen to them, because it's difficult, for me, at least, to grasp their sample problems or remember the equations and stuff without picturing them in my head, etc. So that's my $.02