Pandoc is a haskell library and a command line tool, that can convert markup from one to another and it does it pretty well. Until now it supported quite a few markups, but not orgmode. But now, Orgmode support has been added! Yay!
But, it can only read from other formats and write to org-mode format. The other way around, is not possible, but you can do that straight from org-mode, right?
I've often felt the need for an org-importer and hence decided to do something about it. I stumbled upon Pandoc, when I was moving my blog, and found it pretty neat. After, yet another request for an importer, on the org-mode mailing list, I decided to look at Pandoc. I was somehow under the impression that it was written in Python. But it turned out, I had to learn Haskell! A good excuse to learn a new language, eh? I brushed through a tutorial for a couple of days (and was blown off by the paradigm of the language) and was able to port the RST writer in Pandoc, to an Org writer. :)
You can get the latest version from here