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I don't know.   I have been making websites for a long time.  I've seen google treat subdomains like gold and stack them in the SERPs so that subdomains on a single domain will fill the top ten and push all competitors down.  Then I've seen google treat subdomains like crap, then like gold again. So, don't bet on today's flavor.  Keep in mind that lots of domains have subdomains managed by other people.  Do you think that the actions of those "other people" should make the rest of the domain stink if they are crappy?   If you think that your subdomain should not stink if the rest of the domain is populated by idiots then go ahead and place your big  bet on subdomains being treated equally.  I'm not going to do it.  Do you think that blogspot blogs are treated like a single site?  I vote NO on that.  Do you agree? If you want your collection of content to be guaranteed support for your main site then you better put it in a folder.  I am putting my good content in a folder and staying away from hosts, shopping carts, software, platforms and any service that can't handle putting my content in a folder. Google changes their mind on this type of stuff all of the time.  So bet on what you think is long-term certain and not on what you hear people sayin' even if Matt Cutts is the one who is sayin'.  I remember him posting right here on moz (SEOmoz then) that you could sculpt pagerank with nofollow.  Then Google changed their mind on that and didn't tell anybody. Do what makes long term sense, not what people are sayin'.  I think that smart people are still saying put your  content in a folder.