I’ve found that using dofollow for all links in WordPress comments is generally not good because it attracts unmanageable amounts of spam – basically spammers use bots (scripts, automated programs) to surf the web looking for dofollow blogs. When they find them they come and personally leave spammy comments hoping that the author will approve them. Yes spammers automate spam commenting too – but these are easier to pick up because they are generally less relevant to the content.
What has bugged me about this is that if I reply in my own blog comments then any URL is also nofollowed. Thsi bothers me because I quite often link out to other sites in response to users questions and I don’t want these links to be nofollowed – I’m writing teh comment, I’m placing teh link, so why shouldn’t be considered by Google to be a dofollow editorial link?
The solution to this problem is an excellent little wordpress plugin http://www.everfluxx.com/follow-my-links/
This provides dofollow links for the authors posts. Just what I wanted.