Windows 7 64-bit desktop PC. No major incompatability issues, but I do get problems with the availability of the Norton Toolbar on web browsers. It is no problem in Firefox which I now use as my default. Within Chrome I received a message upon installing NIS that it needed to update Chrome (which it did), but there was no sign of the toolbar. Eventually I rectified the problem by uninstalling and re-installing Chrome. The toolbar has never worked in recent versions of Internet Explorer (and still doesn't), so I have not bothered with that.
With regard to stability, my only comment is that internet pages seem a little slower to load. Nothing major and I have no specific timings - it just seems slower to the naked eye.
Generally however, everything seems hunky dory.
Other than the above, everything is hunky dory.