Here's what I've figured out. I can determine whether I connect as a leaf or an ultrapeer by manipulating my preferences. I have a cable connection, which apparently is enough bandwidth to let me be an Ultrapeer if I want. If you have a cable connection or better and you want to connect as an Ultrapeer, go to Limewire Preferences and try this:
1. In the "Speed" preference, make sure "Disable Ultrapeer Capability" is not checked.
2. Under "Uploads/Basic" set upload bandwidth to 100%. (Depending on how much bandwidth you have, you may not need to go that high.)
3. Under "Uploads/Slots" make sure all three boxes have a number higher than zero. (Mine are set for 50 and 1 and 3. I think 1 and 1 and 1 would probably work.)
I don't think this will change how you're connected now, but the next time you fire up Limewire, I think you'll connect as an Ultrapeer. You'll have dozens of connections. Right now the top of my Limewire window says "...Sharing (6,444M files / 42,967 GB available)" and I've been connected for less than an hour. I am also uploading almost constantly. However, My wife will soon wake up and get on her computer and start complaining about her slow connection, because I'm over here using up all our bandwidth.

BUT THEN AGAIN...
About 5 hrs after posting the above info, I updated to 3.1, and now I'm a leaf again...