Actually there is an open source windows clone, it's called ReactOS, not really what I'd call overly stable yet. Also it's based on the XP/2003 framework, but Seven is just a cosmetic addition to that anyway, there's very little real difference, and the only things that XP lacks, that Seven has, are artificial impediments that Microsoft have woven into their OS. An open source clone would have no such impediments.

As for Ubuntu 9.10, I'm actually having some problems with it (for a change, all the last 5 or so releases of Ubuntu have worked flawlessly for me). My sound card isn't working (had the same problem when trialling Seven too), and seems a lot of other users are having the same problem. I may downgrade to 9.04, or just switch to another distro, if there's no solution within a few days. This release of Ubuntu feels a little rushed to me, looks like they didn't put in enough work on polishing it up.