Whether Linux is usable for a "normal" user depends largely on what you describe as a normal user.

Does a normal user use Quark, Photoshop, Sage, Premiere and a bespoke accounting programme written in 1703 on MS Parchment 1.2? No, in fact, hell no.

A normal user uses a desktop, browser, word processor and a spreadsheet. My wife (Holy ****, a *nix geek who's capable of getting laid... whatever next ;)) is a normal user. I overwrote her annoying XP load with Ubuntu and after restraining her initial wave of anger, she quickly (in approx 10 mins) learnt that a Gnome desktop works *exactly* like Windows for the stuff she wanted to do. Connect to WIFI? Check. Open a browser? Check. Look at Videos on youtube? Check. Update spreadsheets with home finance information? Check.

Normal users don't recompile Kernels. They don't install drivers, on any platform. They call us, Reg readers. And if you don't get called it's because you're rubbish ;)

Personally, I don't care what OS you use, but it does make me laugh when people spend £100 or so on an OS as bad as Vista. There are bad Linuxes too, but at least you don't have to pay for them.