Can't say it much better than The_Red_Shoes did, so I'll just repost it:
"Our goal for sponsored communities is to give businesses an opportunity to connect with their customers, give you special deals -- free stuff! -- and information. More and more companies are moving to blogging as a form of communication -- people are starting to understand that there's a huge potential for conversation, and they want to reach out and have that conversation somewhere where the tools are already built in, like LJ."
Jesus, that's disgusting.
Fortunately someone has already come up with the idea of viral anti-marketing:
How many pages of NO can 10 million users generate? Let's find out!
If you don't want more sponsored corporate anything in LiveJournal as seen here in this post, leave a simple NO in the comments to that post and then pass this on to your flist asking them to do the same.
Pass it on.
ETA: lysana pointed me at this clarification of the original post. I don't particularly want sponsored communities on LJ, but what I really object to is the notion of "sponsored features" that paid/permanent users would have to view ads to use. Note that I consider "this feature sponsored by foo" to be an ad, so I'm not entirely sure my objections are covered by the clarification, but it helps.