I am developing a new blogging platform where user can register and create a blog [like blogger or wordpress]. My Question is "Is there any difference in allowing user to create blog URL as http://username.<mysitename.com and http://mysitename.com/username"..How does it different as far as google page ranking and indexing concerned. Does google penalize my site if some one uploaded some duplicated content if I used http://site.com/username Write now I am using http://site.com/userid/... approach..
it changes over time. Once, Google regarded subdomains just like 'real' domains. Then they seemed to favor subfolders for a bit. As subdomains are intrinsically more difficult to set up than a subfolder (you need control over your server to script it) they will probably always carry a little more weight in general.
As far as i know, google treats subdomains as different domains and the sub folders as same domain. More over, i dont want to create a blog myself if it is a subfolder in a domain instead of a subdomain. A sub domain gives the feeling of own-ness.