taken several classes at the UC Berkeley extension. i did an on line biology course that i used to get credit for at my current job. this class was as good as you could expect for an on line class--you get out of it what you put into it. i also have taken art classes at the art extension, which is part of the ASUC. i found the art extension pretty fun. the people, including the staff, are a lot of fun, laid, back, and very helpful.
a con of taking classes at Berkeley though, would be the fact that parking is so hard in the area. you really have to plan for extra time to just drive around and find parking.