When I use the term MySpace I'm including similar sites like YouTube and others.

What they offer - they will host your content for free and they market themselves for you so they become an obvious place to look for a band. For those on limited resources or ability they offer a website presence for your venture. To fund this they display advertising.

From the music business view they are a search engine, you want your content to appear when people look for you. So submit content and when people find you sell your venture, encourage them to your website and turn interest into custom/fan

The unknown artist/group that's suddenly suddenly discovered via MySpace is more media story than solid fact. Unless you have a novel idea or pots of money don't worry about MySpace campaigns. If you have a very large database of fans then you can encourage them to boost your MySpace ranking by becoming friends and all that.

From the music business view MySpace et al are search engines - submit your content, design your page to drive people to your website because that's the best place to sell your idea and turn them into money.