Off by default yes but blocking trackers is also off by default and as soon as you hit the settings they promt you to opt in. And if you're opted out you can be sure that every few weeks to a month Ghostery will update and try to get you to mess with it's "redesigned control panel". This is less annoying than YouTube's constantly trying to trick you to sign up for G+, but it's still annoying behavior that 90%+ of addons avoid.

And they downplay the sales angle [1] and fail to mention that they sent every url you visit back to their servers in the clear [2]. That's fine if it doesn't bother you but it strikes me as shady and disingenuous on Ghostery's part. Anyone who feels likewise should check out Disconnect [3] which is open source and breaks fewer sites.

[1] Although not as egregiously as in the past. Here is how they originally pitched GhostRank: Ghostery provides reports to Evidon about advertisers and data collectors, which Evidon then provides to regulatory agencies like the Better Business Bureau (BBB) and the Direct Marketing Association, parts of the Digital Advertising Alliance (DAA)[2]. These agencies then use those reports to monitor how Online Behavioral Advertisers operate and, when needed, refer them to the Federal Trade Commission.

[2] http://wtf.cyprio.net/ghostrank-logs-every-visited-url-in-cl...

[3] https://disconnect.me/