I've had a very mixed experience with them....with my cable business bad. I had a dental site some years back and it worked great.
I have used goclick. well for keywords like affiliate programs and business opportunities you get lots n lots of clicks but no quality leads really. Other keywords well the good thing is they are much cheaper than google but it takes a really really long time to get clicks, atleast thats what my experience was. They do have an internal click fraud checker and they do refund money if their internal checker finds click fraud but honestly i dont think it works well. They refunded 8 cents to me once.