Uvumi.com is a music web site with a focus on artist promotion and social networking. According to their About page, "Our mission is to empower artists, promote widespread creation and consumption of art, and add value to the artistic community." It's geared at helping artists get a platform, boasting a "clean and useful social profile that is highly optimized for search engine indexes." 
Since I'm not a musician, however, I can only rate the site fairly from a listener's point of view. So for an easy guide, I've narrowed down my criteria to six categories: appearance of the site, ease of finding music, ease of buying (or, if the artists provide free music, downloading) songs or albums, tech support for problems, general community, and extensiveness of the music library.
Appearance. Uvumi is a cleanly designed site, with categories like "Charts" and "Music" accessible from the main page. The word uvumi is Swahili, and "means low sound, rumbling noise, murmur, or hum."  For a new user, the main page seems to toss a lot of information on the screen at once, and can be a bit confusing to navigate at first. Once listeners start to get into the site, however, their friends' activities (making new friends, becoming a fan of bands, favoriting songs) show up, drawing them into the site's various features.
Artist and listener profiles are very functional; artist ones provide a bio, photos, songs, contact info, and more in a visually appealing way. There's a space for other users to leave comments on profiles, and the site gives artists the ability to create professional-looking press releases. Users can also start a blog on the site within seconds.
To sign up, artists must first register as themselves, and then create an account for their band. This resulted in some confusion at first, but seems to work out quite well in the long run.
Finding music. The charts and search functions make it simple to find one's favorite artists, and listen to similar music by genre. Users can favorite songs by adding a star to them, or earmark them for use in their playlists.
Buying/downloading. Currently, it's not possible to buy music directly from the site, but with contact info readily available on artists' pages, users can click through and buy music from other sites. There is an option for artists to allow a free download of a track. Some users have expressed the desire to upload their music for sale or buy it from the site, so whether or not it'll be implemented in the future remains to be seen.
Tech support. The tech support at uvumi is phenomenal, the best I have ever seen from a company. The staff answers their e-mails promptly, and users can send a twitter to @uvumi if they need help, and often receive a response in minutes. The staff outlines plans for the future and necessary maintenance work openly and well in advance. 
Community. There is a vibrant community going on at uvumi from "thesixtyone refugees." It's simple to request friendship, become a fan, or leave a comment. The ability to upload multiple photos and contact info makes this site a contender to be the Facebook for music lovers.
Music library. As little as a week ago, the site didn't have very much to offer, but multiple new artists are appearing every day. Right now some of my favorite artists aren't on it yet, but as word spreads about the site, that could change.
Overall, uvumi.com seems to be a great resource for community-oriented musicians and listeners to gather. It's obviously still a young site and is rather small right now, but the staff seem dedicated to making users happy.