Right now, I run a blog at wordpress.com - as you may, or may not, know, you can't have ads on your blog there, seeing as it's free hosting. Having decided that I want ads on my blog, I've decided to export it to a privately-hosted server with wordpress.org (which allows ads.) It is as simple as me getting my domain, exporting the blog (xml file), and then importing it to my server. Now.. Is that considered duplicate content? I'm planning on deleting the wordpress.com one immediately after it's moved. Will that cause any trouble? Thanks.
For the period of time that both site's URLs are in their index then YES it will be considered duplicate content. When you delete the old site at WordPress.com, the old URLs should start throwing 404 errors when the search engines request them unless WP.com does something to prevent this. Evenentually your old URLs will get dropped from the index at which time if your new domain's URLs are the only copies of your posts out there then the new URLs should be given originator status. But if other sites have been scraping your content or grabbing copies via RSS and posting on their sites, you'll likely NOT get dubbed the originator. This is the problem w/ WordPress.com, BlogSpot, and other free blog and web site hosting sites. Not only are you limited by their TOS as to what you can do like advertise, limited by the amount of control you have (which might, say, prevent you from having a custom 404 page), but you ALSO get ROYALLY screwed should you ever decide to move your site to your own domain hosted on your own paid web host. They give you NO way to 301 redirect requests for your old URLs at the free host to your new URLs at the new paid host. Unless you just don't know better or you're willing to start over from scratch with a brand new site with no backlinks when you decide to get paid hosting, you'd have to be crazy for knowingly EVER sign up at a free host.