This excellent New York Times article outlines how Myspace evolved from a spammy junk site to one of the internet's top destinations, second only to Yahoo in page views according to several sources. I remain skeptical Myspace has more traffic than EBAY, but clearly they are huge and growing at a jaw-dropping rate from last year.
HOWEVER, Myspace is NOT hugely profitable with only 1/20th the revenues of Yahoo, the top online destination in terms of pages viewed.
I think the explanation is simple – Myspace traffic is dominated by young onliners who are enthusiastic and spend many hours per day online but have little interest in most advertising and not much money to spend. I doubt this will change.
We've noted at our US history site, which appears to get most traffic from school searches, that it is hard to match users and advertisements.