Has anyone tried this anti tracking addon

[#1]

http://www.ghostery.com/about
Seems an interesting feature but I am not sure of the benefits

[#2]

Interesting enough to have a quick look. First thoughts are that it's biased towards monitoring for US based trackers - which I suppose is a given seeing that one of it's main selling points is to help US advertising companies conform with their US regulatory obligations (see http://www.betteradvertising.com/about_us.html and http://www.betteradvertising.com/our_mission.html.
Having said that many of the more common trackers are US based (eg Google Analytics) and it does seem to be blocking trackers on a number of sites I tested it on with Firefox (eg thinkbroadband.com, tomshardware.co.uk, dyndns.com). One thing to beware of is that some sites rely on tracker behaviour to work so blocking them could cause them to stop working in some way (see the ghostery forum for examples of this http://getsatisfaction.com/ghostery/topics). Oh, and it doesn't work with Opera.

[#3]

I had been using Ghostery for a while and at one point I would have highly recommended the add-on but sadly the original creator sold it to a commercial company, that used to be heavily involved with online marketing but are now setting themselves up as some kind of regulator. If you are to use it make sure you have the "send anonymous usage statistics" un-ticked.
I have heard the addon NoScript is much better (https://addons.mozilla.org/en-US/firefox/addon/722/) I haven't tried it myself yet though