MySpace yes, but the problem is not how much traffic, it is how targeted this traffic is..
There is no point in having your advertisement being shown 1 million times to people who are not interested, it is FAR better to have your add shown to 10 people who are interested in your product, more chance of a click conversion!
The reason i say this is because places like myspace and facebook and bebo, all of these sites are web2.0 which is whatever people want it to be! You cant target these areas unless you offer similar products/services..
So in light of your question after a long winded post (apologies!) but it really depends on what you are advertising..