Is this a problem? For getting the backlinks and content there indexed?
h t t p://johndoe.livejournal.com/product-name
h t t p://johndoe.blogspot.com/product-name
h t t p://johndoe.tumblr.com/product-name
h t t p://johndoe.vox.com/product-name
The content on each is different, but the same theme.
But, I was wondering if the user names in URL (being all the same) is a problem...