I don't agree with having a five-point scale. The reason for the success of sites like FML is the simple yes/no voting system.
For those sites, I'd agree with that. They're pretty flippant. But this is different (I felt that people could make career decisions partly based on these votes) and I found it uncomfortable choosing "Awesome" for an idea that I thought could be OK, maybe.
I'm not so sure on a scale. I think comments with why yes or no would be more useful (working on it).
An already done flag is an excellent idea though! OR could this just be a NO + comment with link?
I'd vote for Done Already that shows a link box. And, of course, comments.
Comments are now in. Just click the little + button (creating a more obvious link in a minute)