I think this is a good plug in however I have disabled it on my sites due to an unforeseen problem.

When Google crawls my sites it sees Invalid Security Tokens as a result of the comments plugin. This generates 1,000's of 404 errors as reported by Google Webmaster.

Google in their typical response says it "should not" be a problem for ranking, but "should not" and "is not" are not the same. And they don't pay my bills. So I'm not going to use it.

The developer suggested I "nofollow" the lines in the code that create this error (Which is not their fault, it's Google). The problem is Google elects to sometimes see the "nofollow" and other times completely ignore it.

Until Google figures out how to treat their own "nofollow" attribute (Which they pushed so hard and now seem to be abandoning... I'm left to play it safe and forget about comments on my Joomla Sites... which is too bad because I really like the star ratings and social bookmarking features).