How about a list of all the things that really work great? I've been using Linux on the desktop for nearly 20 years and I'll have to say it's fantastic, despite the occasional headache, which seems to be at a far less frequency than other major desktop operating systems.
I'm guessing you're relatively tech savvy and enjoy troubleshooting (within reason). Most people aren't, of course.
The main thing a non-tech savvy user needs to worry about when considering Linux is to generally understand that hardware support lags a bit. So they should do a few web searches on the make/model of hardware they want to use + 'Linux support' before they dive in. If they don't see page after page of glowing success stories, they have their answer and should steer clear of that configuration for the time being. If they do see lots of success stories, read a few of them to see if their eyes glaze over at what is written or if it seems pretty straight-forward and they can follow what's being said. No tech savvy required.