an ultrapeer helps people connect to the network. LW Basic users need to be connected to 3 ultrapeers, pro users 5. Search messages tend to travel across them. So in a word they are go-betweens. Someone who is an ultrapeer gets the advantage of being able to connect to many ultrapeers themselves. They can usually also download from many more hosts per file than the average user.

As I mentioned in my previous post, some days search returns are poor. But this is usually only temporary lasting a few days or so.