After installing windows for my job I also installed the soon to be released Ubuntu 12.04. I didn't expect it to go too well as Windows took me a long time to install and nothing worked out of the box there. Windows was quite a pain to get up and running with all the hardware this nice laptop comes with.
I have to say that I'm pleasantly surprised as with Ubuntu everything worked out of the box. At least everything I tried and used. So far I didn't use the Fingerprint reader as well as the SD card slot. I wonder why Dell doesn't offer the Latitude XT3 preinstalled with Ubuntu.
The only minor problem so far is that not all special key functions work correctly. But all the important ones and most of the not so important ones work just fine. The multitouch trackpad does even work better with Ubuntu as two finger scrolling in windows is something you need to get used to. It does work as expected in Ubuntu and has somehow a small input lag with Windows. It's rather annoying as its hard to scroll anywhere with that.
It starts up to the login screen in 10 seconds, which is half of what Windows 7 uses. On my desktop at home I have autologin active as I'm the only one using it. As the laptop is mobile and can be stolen more easily I login every time. Also I encrypted my home folder which requires you to login as this would defy the purpose if you autologin. After login it takes about two seconds to a fully working and usable desktop. It's pretty damn fast with Ubuntu 12.04. And looks beautifully at that. A co-worker of mine was quite astonished at the speed and look of Ubuntu. I think he would like to have his Windows/Mac box be a Windows/Ubuntu/Mac box now.
I did draw a bit with the screen being capable of pen input. It's really nice to see what you draw directly under your pen. The overall experience is better (mostly faster, more responsive) on my Bamboo Fun Tablet. Besides that the tablet has more features. But for rough sketches, quick diagrams or annotating something its nice to have.
Overall I'm pretty satisfied with how Ubuntu performs on this nice Dell Latitude XT3 laptop. Besides a few minor things there isn't any real deal breaker here.