I own a site that covers many nice subjects. To assist in advertising I have purchased several domain names that match those subjects and used my godaddy acct to 'mask' the domains on top of the url and add in meta keywords etc.. Will this be considered duplicate content? i.e. instead of: www.mysite.com/thispageaboutstuff.com I use: www.siteaboutstuff.com Internally on the site, if someone went to mysite.com first, they would use the first url. Externally, like a craigslist ad or something, they would use the second url - more memorable that way.
Definitely duplicate. Consider using a 301 redirect, instead, from the www.siteaboutstuff.com address to www.mysite.com/thispageaboutstuff. That way you'll concentrate all the link love in one place, and avoid any confusion with the search engines.