I agree buying a Mac isn't always feasible, unless the user is ready to upgrade their hardware anyway, but installing Linux is very feasible with normal home computer users. You do your customers a disservice if you aren't asking them what they do with their computer, and if they'd be willing to consider it. I've found that the majority of "normal" home computer users I know don't use it for much more than web-browsing (and web-based email), Skype, downloading pictures from their camera, and maybe a bit of light word-processing. Lay out the pros and cons, and let them decide.