I have to throw my opinion in to the hat..
I had been hearing good things about ubuntu lately, and having a bit of spare time on my hands, and not really giving Linux a go before, I decided to chuck ubuntu 9.04 (Jaunty) on to my main work PC.
Now, I had tried the OS through a Live CD so I knew what I was expecting, but having it as a 1-and-only OS was a big step. Especially when my work PC had been running XP all along, and the spec is well "performance overt".
I would like to say I found the whole UI and layout very intuitive. I particularly liked the Applications menu bar, and the administrator and preference menus (you can tell I'm new to this

) I also liked the way you can search for apps, and install them direct from the Add/Remove window.
...oh, and it added all the network printers with 1 click.. result.
I will say I had some initial problems with nVidia drivers giving me an "out of range" message, meaning I couldn't set the resolution above 800x600.. but that was easily fixed. Certainly, it wasn't enough to taint my view of things..
Possibly the biggest regret was not thoroughly checking Office 2007 compatibility before making the leap. By that, I mean OpenOffice 3 seems to handle most of the files I throw at it, but it will completely die if I throw a complex .xlsx (excel 2007) file at it.
It hasn't crashed or hung on me yet, and as I'm a complete newbie I've been pretty much digging through every menu and pressing every button, so that's a bonus.. my only regret is that it looks more and more likely I will have to dual boot Windows just for the Office apps.