For some reason glxinfo does not report any multisample visuals on any of my machines. glxChooseVisual does not return any either. Did something change? This is happening on a 7800GTX, 8800GTX and Quadro FX4500. The extension is in the available list. Also nvidia-settings --glxinfo DOES show visuals that support multisampling. This used to work - but at some point this behavior started - haven't really paied attention to it...
I have seen one or two posts that sound similar to this but with no definitive answer.
I have attached the requisite bug-report log.