First of all, it's not a waste of time. Linux provides me a very nice income.
Second, knowledge is always good. Anything that knocks a chunk out of a monopoly (MS / Apple) is a good thing.
Third, It's *my* computer--not Microsoft's, and not Apple's. That means I have total control over it--patching, updates, which OS to run, and what software I choose to install (without being nagged that it isn't "approved").
Okay, so you are a Linux consultant or use it for work, fine. But for the common computer user, it is a total fail. That is, unless they have deep pockets or a personal relationship with you.