tedster - 12:25 pm on Dec 11, 2008 (gmt 0)

...it will also get the link juice from the main site

Assuming, of course, that there are links. There's no magic that spills over to a hostname just because the root domain is the same.

Subdomains figured heavily in some types of spam that Google needed to get a handle on - the total spam technique also used the fact that Google was indexing root pages very fast, even though the rest of a site would usually be sandboxed for quite a while. So the spammers said "How can I get tons of root pages? Use tons of hostnames (subdomains)."

Maximillianos is on the same track as I am here. A legitimate subdomain today often gets treated as something of a hybrid between a totally different domain and a part of the main domain. It's not 100% uniform - there are blogging platforms that offer each user a dedicated subdomain, for instance, and for those there's more of disconnect between the root domain and the user's subdomain.

So you're not likely to dominate an important SERP today by grabbing more than two positions via subdomains.