I’ve been a supporter of OSS/FS for years, and used what I could even before I finally made the switch to GNU Linux this fall as my desktop operating system. This long article, Why Open Source Software / Free Software (OSS/FS)? Look at the Numbers!, not only gives the standard reasons for migrating, but provides numerical support for doing so as well.
Do I think that desktop Linux is ready for the masses? Judging by one or two recent questions I have been asked by people (who unfortunately think of me as some sort of computer expert) I am not sure that Windows is ready for the masses.