Useful plugin, not sure about privacy Rated 4 out of 5 stars
I've been using the WOT add-on for about a year on most hardware, and it's both useful in steering one away from malware or useless sites, and also a useful way to report hacked sites used for phishing and so on. In the UK, the Bailey report on protecting children online mentioned kids' ideas of pressing a button to report an inappropriate site, and MyWOT was already one good implementation of the idea. The add-on has a pretty clean design, and is not too intrusive.
How much do I trust the Web of Trust? A bit. The categories are fairly broad, and "trustworthiness" can might everything from whether the author of the information has relevant expertise or has a conflict of interest. However, if the site has a vulnerability then someone could be maliciously uploading content to pages on the domain; hence I have to give otherwise "good" sites the lowest rating, and I'm sure many other IT professionals do the same. I am seeing a few subdomains where it looks like a phishing gang have managed to game the system slightly to make a new site appear trustworthy, so it's not perfect.
One slight privacy worry is that it sends the domain name of any page you are viewing to WOT. For Google Safe Browsing, there is less of a privacy issue because Firefox downloads the data and compares the location to that. OK, WOT don't retain the data, but it's not ideal. There's an option on the privacy page to make make communication with WOT use SSL but it's not on by default.