Ive used trafficswam, i used there 'link box' feature. u show several links on your site and your site recieves clicks for every time a link is shown. I had 4 links showing on every page of my forum... with 100 visitors viewing an avg of 10 pages a day. Thats 1000 free and easy visitors, mind you they werent very targeted, but it definetely helped by Alexa ranking. Which meant my ads started paying more
As my forum grew i got rid of the link box and filled the space with ads. But it definetely was helpful at the start of my site. I wouldnt continue using a traffic exchange once my site started taking off.
I use linkreferal now, it sends me about 20 people a day. & i get the odd review of my site which is handy.