Don't bother Googling to snoop about your preceptors, use the BOMEX website instead. Any court proceedings are posted in delicious, yet alarming, detail. My first preceptor out as a MSIII had a scary rap sheet a mile long. Too bad I found out too late!
As for clinical ed, it seems sometimes like they were put there just to test your patience. However, it seems that being very firm will help you get your way; they will give you the shaft if you let them. They're just trying to do their jobs, which I'm sure get ridiculously complicated, but it just means that attention to detail is lacking sometimes. Like when I'd have a preceptor cancel a rotation (which happened way too much) they would just stick me in with a random person (and usually a crap rotation) instead of emailing to tell me what happened and asking if I had any preferences as to where to go.
I would say that the best way to avoid clinical ed is to harrass the upperclassmen, get names of both good and bad docs, and request them specifically.