Ubuntu isn't that bad, Firefox, Evolution (email client) and Open Office are very nice. I ran Ubuntu in Parallels on OS X for awhile and liked it. Ubuntu will get the job done but it does not have the polished look you would expect in a 2007 app. I think other "home apps" could use improvement - photo editor, mp3 manager, video manager. Most linux apps are ugly, IMHO.
Get one of the new color Dell's (black looks cool) that supports Ubuntu and you can get in-home hardware replacement (next business day - after you talk to the support guy in India or Argentina over a shitty VoIP connection) including a laptop. Dell has done a good job at building a support infrastructure to do these on-site hardware replacements. I have been impressed when I had to use them. Apple should use this same support model.
System76 looks like they have a full hardware (laptop, desktop, server) offering with Ubuntu. I am not sure of System76 operational hardware support model though. Will Dell or someone else eat their lunch in the market for Linux based systems? Will they be around next year? who knows.. But they are worth looking at and asking them a few questions.
BTW, Here is a better Linux IM client (it is not as ugly).
So to recap your questions:
1. Better corporate based hardware support to Linux is available even on laptops now.
2. Ubuntu has done a better job at asking: what are the core apps that need to be on the desktop. The other options is to just install the OS with only what you need. Easy problem to solve.
3. I 1000% agree with you on getting work done vs. supporting or managing the system. I think you are going to run into this with any OS you run and not likely to go away any time soon. Pick your poison.
4. There are better IM clients now than ugly GAIM. See above.
You can always get Vista and turn on all the eye candy and repeat: this is OS X, this is OS X, this is OS X. j/k
The last time I ran linux on my desktop, it had the following problems:
1. It didn't really work right. It sort of worked, but not really. Things were broken. Things weren't well supported. Things like the mouse. It actually didn't click exactly where it pointed some of the time. And this was an IBM laptop. Not something oddball. And some hardware was tweaky... like wifi adapters that had to be unplugged and replugged sometimes in order to reload the drivers.
2. It came with WAY, WAY too much shit by default. Every jackass who had ever written an open source GUI application had managed to get it placed in the default menu.
3. Things needed to be screwed with a lot. A lot of tinkering, a lot of configuring and compiling and updating. Systems Administration. People who run linux desktops like to configure stuff and seem to enjoy applications like mutt that are way too feature rich and are basically useless if you don't want to invest a few hours into getting them to work right. I don't want to do that. I want basic shit to just work. I have work to do. I want to get it done. My computer should enable that. The reason I'm sick of my mac is that its getting in the way.
4. Firefox was fine, everything else was crummy. The IM clients were just downright ugly.
RE: Desktop Linux