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I thought Category would get more value if it was the subdomain. However, I don't know if since G treats it as a separate website, that I am spreading PR too much.
IMO, Subdomains make sense for big companies that offer multiple services -- Think shopping.yahoo.com, search.yahoo.com, etc. For smaller Web properties, you run the risk of diluting your branding if you're not already big and well-known like yahoo.
Jim