I've tried it twice, and both times it was a waste of money. I got maybe 5 extra views a day out of it, a favorite here and there, but no sales. I'd rather spend my $5 on supplies than on search ads.
However, I have heard a bunch of people have had at least a little success with these things. I was tempted to try them again, but I figure with all the posts on the forums and being active in the teams and blogs and yadda yadda yadda, I can make up those 5 measly views a day without having to spend any money.