Hello I personally hate rel=nofollow. Yeh, it serves a purpose, but its annoying for link builders And i think its kinda rude. Soemone posts a nice comment, and you're basically saying "Thanks for the feedback. But you're not getting a link back (in googles eyes anyway)...." So i did a quick guide on http://london-seo.com/remove-rel-no-follow-word-press/31/ on how to remove them. It is only a couple of files you have to edit (sorry, no plugin for it. It isn't worth the time, for me!) It would be interesting to see your view on rel=nofollow. I know what it is for, but if you moderate comments anyway, hopefully they won't become full of spam.
I moderate all of my comments ion my blogs, and I removed the nofollow a few months ago because of that. I don't mind giving other websites credit for commenting on my blogs. Personally I hate the idea of nofollow. It's a search engine's way of getting web site owners to identify uncontrolled content and links. The search engines can figure that out for themselves. As long as you comments are moderated, then nofollow is absolutely not needed. If you have tons of unmoderated comments, then for your own protection, I would use it. Also, make sure you use akismit, as it block just about every unwanted comment you ever come across.