You know how nofollow links do not pass PR but also don’t devaluate links on the page? Well that is not true anymore. Now when you have a bunch of nofollow links, the nofollow links still absorb PR and devalue the dofollow links! What happens to the PR? Well, it sort of just vanishes. So if you have 96 comments on a blog post and 4 dofollow links within the post, those dofollow links no longer receive 1/4 of the pages PR per link, they now receive 1/100 of the pages PR.
So in a sense all those links are consuming PR without passing it on! This is really not good for blogs. You might as well make everything dofollow because it won’t make a difference. I can see some blogs disabling the use of posting your site url in the comments, or just making all comments dofollow. I’m not going to change anything personally since I don’t get a ton of comments 
Oh yea, and I wouldn’t bother with PR sculpting anymore, with these changes I don’t see how it would make a difference. PR sculpting is basically making some links on your page to other pages on your site nofollow and thus making the links to other pages stronger to make them rank higher, if you didn’t know already.
This is one of my sites where I am far from an SEO nazi. I am on some of my other sites though On a side note, any of you check out bing.com? MSN’s new search engine? It’s pretty neat. I sort of liked the name Kumo better, but that’s their decision
References
http://searchenginewatch.com/3633972
