There a belief that Linux is hard to use. It more down to the distro you install. LinuxMint looks and acts almost identical to XP - without the snazzy blue taskbar and rolling green hills
Put it this way... My mum can use it. So I reckon the people who share wouldn't even notice it had changed.
It does bring fresh life to old hardware. I just got given a pc found in a cupboard in a new house. It had a knackered PSU, I've replaced that and now it works. It was pretty slow running before but it feels pretty rocket-fuelled now.
It's gonna become the backbone for an arcade machine I'm building...