Originally Posted by ROHOST
I am not sure it can help at the page rank, in fact i think the opposite. Maybe it was easiest way to handle the subdomains, not a part of marketing.
Subdomains contribute both to alexa ranking and google ranking as the main domain name is listed in the site.
As far as marketing - you're getting your main domain out there even further (just like geocities and their sites - geocities reaped the rewards of people signing up). Same effect.