I second that. I have been using them for 5 or 6 years now, for various sports and definitely notice a difference.

I have used the "skins" brand and I am more than happy with them. They are a little more expensive here in the US than Australia but I have continued to buy them. As Racer Ex mentioned they differ from regular and even medical tights as they have graduated and localized compression.

At the Green Mountain Stage Race last year I put them on basically straight after the finish of one stage, slept in them, and took them off just before the start of the next days stage. It definitely made a difference. Anecdotally, by the 4th day I was much fresher than I expected and compared to many comparable riders.