I'm pretty happy with my Ubuntu installations.
I've had it on my mothers laptop for the last year, only got a call from her twice. Needed a few extra minutes to set up (decss2, gmplayer), but after that it is almost more user friendly that windows. Samba just worked, as did the wireless. The package management system is great, though they do have a few old broken packages still floating around, especially for x64 architectures.
As well it's on the GF's laptop and I have an HTPC install (Myth) in my living room, and a Samba/Apache server at work which does great work in it's mixed enivronment (windows/linux workstations... yes ubuntu on them as well). There is the standard issues with ATI drivers, but with some effort they can be made to work excellently (or you can just use nvidia based cards).
I'm running a pretty stripped down version of slack on my personal machine (but I have only a few things I really need it for), once again great.
My favourite bit is the wide range of free software availible. If you have a need for something, it's usually out there already, and very powerful at that. With a decent system, it even works great gaming.
I have a hard time justifying expenditures on windows, unix, or any other software when there is open source stuff availible that is just as functional, sometimes more. Of course, such decisions are sometimes made without my input (DAMN YOU CITRIX!).
And linux is indeed unix like, but I'd shy away from calling it a knock off.