Yes, I've done it.

For my second novel, I adapted "The Long Road Home" for publication and my new publisher loved it. After four very extensive rewrites and edits later, it's now in the typesetting stage and I should have a cover design soon. (Can't wait to see it!

) It's going to be released late this year or early next under the title "Between the Lines." (They're even doing an unabridged book on CD. Yay unabridged!)
Because of the extensive rewrites, not much of my original fanfic is the same. It's more suspenseful and deals a lot more with the bad guys than LRH did. Villains are different, too, and there are different subplots. Anybody who has read LRH probably wouldn't even recognize it as the same story. But adapting the fanfic gave me a good, solid story to start with. So yes, adapating fanfics can be done!
If you're looking to go that route (publishing), I'll tell you, it's not for the faint of heart. This is my second novel, and it's worse than natural childbirth. I have enough rejection notices to wallpaper my house. You have to be very thick skinned and as iron-willed as can be to keep working at it.
If you are shooting for the national market, you'll need an agent. None of the big national market publishers will even open your manuscript envelope if it's not submitted through an agency. And I'll warn you, getting an agent can be even more difficult than finding a publisher. (That's because a good, reputable agent will have a lot more connections and you'll stand a pretty decent chance of getting published because of him/her.)
What else do you want to know? Email me and I'll answer any question you want! I'd be happy to put another fanfic writer on the road to publication.
