I have several old repositories from projects that I don't plan on working on again, unless something extraordinary comes up. However, on my home page and my user profile, they still appear, sorted in with the rest of the projects, and in my "Repositories" dropdown menu. I don't really want to delete them on the off chance that they may become useful someday, but I also don't want them mixed in with the rest of my more important repos.
It would be useful to mark repositories as "old", "abandoned", "mothballed", or some other indicator reflecting their unused status. Mothballed repositories would be sorted at the bottom of the home page and user pages, and not appear in the "Repositories" dropdown. This is more of a UI change than anything else.