I think gitfiddle would be a great name for a service that let you quickly share unnamed, temporary git repositories, showing them to other people, then taking them down, without the friction of GitHub.
Like a git pastebin. In fact, I think gitbin would be better. gitfiddle should be a service where you could do all this, but would also offer ways of messing with the repository (doing interactive rebases, for example) from the web interface.
Github Gists are close enough to what you describe sans the interactive rebase. You can create multiple files at once, all edits made in the web interface are committed to the repo, and all of it can be cloned and used with "real" git at any point.
Like a git pastebin. In fact, I think gitbin would be better. gitfiddle should be a service where you could do all this, but would also offer ways of messing with the repository (doing interactive rebases, for example) from the web interface.