A couple weeks ago, the news that Google treated the distribution of PageRank for pages with nofollow links differently then they would other pages. As explained then:
If you have $10 in authority to spend on those ten links, and you block 5 of them, the other 5 aren’t going to get $2 each. They’re still getting $1. It’s just that the other $5 you thought you were saving is now going to waste.
So Google's Matt Cutts finally wrote a detailed blog post on PageRank Sculpting that discusses what Google does and doesn't do. Go read the whole post when you have a chance, it is very important.
This has been in place for about a year and no SEO really picked up on it.
To my question of "Are Blogs Doomed With NoFollow PageRank Sculpting Issue?" Matt replied:
Q: Okay, but doesn’t this encourage me to link out less? Should I turn off comments on my blog?
A: I wouldn’t recommend closing comments in an attempt to “hoard” your PageRank. In the same way that Google trusts sites less when they link to spammy sites or bad neighborhoods, parts of our system encourage links to good sites.
SEOs and webmasters are simply not happy. The bottom line is this is how it has been for about a year and I doubt it will change.
I am not going to summarize the comments in the thread, simply cause I am not feeling all that great, but I'll link them for you. There are some interesting comments in the thread and in Matt's post.