Board Thread:Skyrim/@comment-13364426-20130725151958/@comment-6881629-20130725154708

Separate saves can be kept on diffrent storage like one on a hard drive one on a memory card (maybe on USB stick too you can on my PS3) and if you can one on the cloud. If you have a memory card or USB stick maybe that can be used to copy and move saves across your profiles too.

As for DLC across profiles i would expect them to make you pay for it all over again as i would think its locked to you profile but if that was the case you would have Dragonborn on both.