What's the point of the OS question on the registration page? GR is web based, so it should work in any browser. Or is it to help people pick projects?
If the second option, it would be better to tell people their choices may be limited (also gonna be true of Mac people) rather than dumping them back to the sign up page and telling them their OS isn't supported. I'm rather successfully running BOINC on Linux. Please don't make me switch my home machines back to Windows.
I'll complete the registration as a Windows user since I do have a Win box at work (and I could switch a home box back).
BTW: I'm using an existing GR account because I keep everything BOINC under one email address, including this dummy FB account.