Pretty good Rated 4 out of 5 stars
Pretty good. I had written a review complaining that the toolbar icon kept disappearing, and my Flash cookies were not being deleted upon exit, and was written back to be informed that the beta versions fix this (5.05 right now). Okay.
It does a pretty good job, allowing you fine-grained control over every tracker, cookies, and LSOs (super-cookies). Plus stuff like scanning images, iframes and the like for the paranoid (Tip: use Collusion's data to tell how well a security add-on is working).
It gets kind of annoying when you can't load a part of a page, but they do have an option to disable blocking for that tracker, no biggie for me (if you get frustrated by this, switch to DoNotTrackMe -- they have real-time tracker list updates). Glad that these kinds of tools are available to the public, and for free. That's pretty nifty. :)