Are you moving the domain name at some point to your blog here?
With the content here you can map the domain name to the blog here. No matter when you move the domain name there will be a bit of an issue with the old links, I moved i think three years ago and once in a while Google digs up an old URL. I had the default .ORG permalinks and some other folders on my old site. you can't do redirects here, one weakness of migrating.
I set the permalinks to match WordPress.COM but the search engines were not quite trained when I moved, Bit of a mess but in the end worked OK
The search engines will be reindexing your site here to the WordPress.com URL, so there will be some loss of rank. Then if you move the domain name to here there will be some loss of rank again
I am not completely sure - Raincoaster is the master of the side effects - but you might be better off moving the domain name if that is what you will be doing earlier so the search engines don't see much of the WordPress.com URL