As it has always been, certain versions of XNA are bound to a specific version of Visual Studio. In case of XNA 4 it is VS 2010. Things like the Content Pipeline won't work in VS 2012.
Farseer (the class version) works with VS 2012 / Win 8. The Samples and Testbed won't because they are build upon XNA.
Since the future of XNA is quite uncertain (aka it is not developed further at the moment) your choices are basically:
- Stick with VS 2010 / XNA 4 and target Win7 / Xbox360 with your stuff. Applications build that way will work under Windows 8 as a Desktop Application since the XNA 4 Redistributable works. But no Metro / Windows RT / Windows 8 Phone / ...
- Go for something else like SlimDX as a Framework. It is more low level than XNA and probably not as convenient. But it is also C#/.NET and Farseer will work. But stuff like SpriteBatch, etc. is gone and you have to code that manually or use third party
solutions like other peoples engines (Flat Red Ball for instance).
- Try out Mono and MonoGame (their version of XNA). This will involve a lot of fiddling around to get everything to work (MonoGame is not yet feature complete and some XNA stuff does not exist). Bonus: You might get your stuff to work on Android / iOS (SpaceChem
did this for instance).
- Wait for the next Xbox to arrive and see if a new version of XNA or some kind of successor arrives with it. But I won't count on that, since MS sadly does not seem to see much benefit in having something like XBLIG anymore.
I'd go for Windows 7 / Windows 8 Desktop development for now and if something good comes out of it I'd rather try to get on Steam Greenlight/Desura/... instead of XBLIG.
P.S. I know that with enough fiddling around people got XNA 4 working in VS 2012. But at the cost of a working Content Pipeline and probably a build process where you have to intervene manually here and there. That is nice as a proof that it can be done
but nothing you'd want to work with imho ;)