It can get problematic when you review an album by friends that you actually do like, too. You don't want to piss in anyone's pockets but you don't want to not share the pleasure, either.
When I started doing a review zine a few years back I had a policy of not doing any bad reviews on the unstable grounds that I didn't want to "offend" anyone. A stupid idea, for the reasons Levas has already stated - I even got to the point where I had to tell someone I wasn't going to review their tape because I didn't like it. Would have been better to do the bad review.
I've also thought for a long time that doing reviews is a bit redundant, anyway. Who makes their decisions on what to buy based on a review? I only write them here because I think the Playlist section doesn't tell me enough and because, fuck it, I like writing about what I listen to. I sure wish more people would use this section of the forum! A bit more insight than just a list of what's on the stereo is something I appreciate.