Those sites that advertise free traffic to your site (i.e. 1:1 ratio) where they send someone to your site if you visit some of theirs... Are they of any value? Is google adsense ok with this? I don't understand the gimmick. Has anyone tried these services?
Those visitors are generally useless and don't actually read your content. It only inflates your hits and wastes bandwidth - they don't click ads or become return visitors. Don't do it.
Traffic exchange from such sites is just waste of bandwidth. Google Adsense works too good with traffic from search engines, as far as I experienced it!