How is Ghostery different from AdBlock Plus, Disconnect, DoNotTrackMe, etc?
Ghostery focuses on transparency, education, and privacy over content blocking. Other than that, the biggest difference is the size of the data collection library. Check out areweprivateyet.com for an open-source comparative study of these tools.
jeevan_500, The chart from the link http://www.areweprivateyet.com/ provided by jamescv7 (from the boxed quote above) is also what I've based my personal use of Ghostery upon. Yes, it's published by Ghostery and thus leans positively toward Ghostery. If you do choose Ghostery consider this advice from FAQs: "..choose “Block new elements by default” in the “Auto Update” section".
Ghostery allows for tweaking while Disconnect is essentially set and leave it.
I do like both, and have Disconnect installed on my wife's Firefox browser beside NoScript. Enthusiasts and written praise of Disconnect (by Disconnect) claim it works better. They both (imho) work well.
Finally, Ghostery blocks cookies in Firefox (unlike Chrome). Try them both (separately) or by disabling one while using the other, and you be the judge.