I use critics' and non-professional reviews to get an idea of the general reaction to the movie. I don't always let that decide if I'm going to see it or not though. If it was something I didn't want to see, I still won't see it even if it gets really good reviews from everybody. On the other hand, if I movie I really want to see gets horrible reviews from everybody then I probably won't see it.
Universally bad reviews are definitely a motivation not pay $10 for it for me, but wait for small-screen alternatives... and I also like to read reviews after I see it as well.