Looks like Google are about to devalue subdomains:
http://www.seroundtable.com/archives/015621.html
Quote:
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News flash from Las Vegas PubCon. Matt Cutts informed us that Google will very soon begin treating subdomains and subdirectories the same in this fashion: there will be only 2 total urls from a domain in any set of search results, so no more getting 3, 4 or however many spots via subdomains. We didn't get any more information than just that basic heads-up.
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The main problem before is that by treating subdomains as a separate site, you could subdomain spam your way into multiple positions.
A lot of high end sites have been doing this - whether intentionall or not - such as eBay.
A lot of blackhat SEO's have also been using this technique, especially with parasitic hosting, where they register subdomains on free hosting companies just for automated content and link building.
This could be one of the most effective spam filters Google have used for some time.
