I've been eyeing Linkvana, too. I signed up for 1waylinks.net about a month ago. It's a low-rent version. It costs $47/month. I've seen some ranking boosts already. However, I may switch to Linkvana when my network gets bigger. Here's the lowdown:

1. You can make 250 posts a month. Any unused quota rolls over to the next month.
2. You need to add one of your blogs to the network. When someone makes a post, it's automatically distributed throughout the network.
3. Each post must be 250+ words.
4. You can post that same blog post to as many blogs as you want within your limit.
5. You can put up to 3 links in each post.
6. There's a spin function, so you spin links, etc.
7. No PageRank or age req't for blogs in the system. However, blogs banned by Google cannot be added to network.