I dug up a promo code I had for 100,000 free impressions on Instant Buzz about a week ago and finally got around to signing up. So, what do I think of it?
It has one major advantage over other traffic exchanges like Traffic Swarm -- you earn credits while you do your regular browsing rather than having to browse a bunch of ads. The Instant Buzz bar is pretty unobtrusive, but the HTML ads that you get with non-free accounts at least stand out enough to be noticed from time to time. I've clicked through a fair number of them.
It has one major disadvantage compared to other traffic exchanges like Traffic Swarm -- the people to whom your ads are shown may not even glance at them, because they're enjoying the same advantage as you. Click-through rates are pretty abysmal. I've gotten a total of 42 clicks, and my 100,000 impressions are spent.
So, what's the verdict? Sign up, because it really can't hurt, and although the value you get is small, the price is right (free). If you've ever been given a promo code but haven't signed up and used it, dig it up, because unless you get a bunch of people signed up under you, you're really going to want the free impressions. I'll be keeping the bar running in my browser (on my PC, which is my secondary computer -- unfortunately, Instant Buzz isn't available for Mac). But I won't be staking my future on making a lot of money off of it.