Creating a community with WordPress MU is not an easy task. I am guessing that most people could only afford shared hosting like me, you will need a webhosting company that would allow wildcard dns. I would strongly recommends Host Gator as I know that they do offer wildcard dns and other configuration needed to run your WordPress MU. Or you could try Dreamhost as I have installed the WordPress MU there before than they works great.
If you do not want to bother about the mumbo jumbo of installing WordPress, uploading plugins, uploading themes, then you can give Blogs.MU a try, firstly they are free if you are using their domain. This is basically a free wordpress mu hosting, but there will be ads and limited control with the free service. I have registered a nice one, http://money.blogs.mu. and the users would be using http://money.blogs.mu/name. Come join my little community.
If you wish to use your own domain, you will have to buy their supporter package that will cost you $9/pack for 10 blogs. Although I am not quite sure about the calculation because 10 blogs meaning you can create 10 MU blogs at Blogs.mu or if we have 9 subscribers to our blog (1 of our own), then the whole package is used up.
You could try out their free service as they have some plugins and themes installed. You will get more with the supporter package. But you can’t ask for more since they are hosting your wordpress mu for free right?
Get your own community and share them here. @ Blogs.mu