From what I have been told here are the only differences. 1.) customizable backgrounds for your journals 2.) Increased viewing of pictures per page (this is not to say that certain pictures are restricted but that you just see more per click) 3.) Polls. 4.)Search engine goes back further than 2 years, however. If you are only looking to see what the latest thing is or know the artist then it is irrelevant.
Personally unless a fan bought it for me I don't think I would get it. I can post my work and make a ranting journal about my life.