I've just started taking simvastation, maybe two weeks ago, 50mg daily, and so far haven't noticed a thing, though some say it takes at least a month for side effects to show up. One of my brothers has taken a variety of statins--he's now also on simvastatin--in an attempt to find one, and a dosage, that's bearable. He had awful knee pains and at times (during or after a run, particularly) felt like his legs were going to buckle. He also feels he had some mood-altering side effects, though my doc says those are enormously exaggerated.
One of the problems of the Internet, for medicine, is that we can go find all sorts of information on side effects and the like, self-diagnosis, etc., and that often we convince ourselves that we're experiencing side effects to drugs because we've read about them. And that the knee-buckling, say, is simply the result of exercising too hard or whatever.
Having said that, I hate the thought of fixing things with chemicals and am definitely not somebody who jumps to take any med...