I won't use Linux as my primary OS until I can use Adobe Fireworks on it as well as iTunes. I do however have Ubuntu folding all day long in VMware in Vista.
It's hard for open-source people to get the big proprietary software companies (Apple and Adobe in this case) to port their code over. And we must wait on them to port it since it is obvious they won't open the code for others to do it.
Since Apple's OS X is nothing but Unix, the iTunes cross-over to Linux would actually be simpler than the already existent port to Windows.
All that said, you can run iTunes in WINE just fine
Relatively simple programs like iTunes should run without a hitch in WINE. I actually prefer
to use WINE for my Boinc SETI@HOME crunching. Never had a single crash or glitch, etc.
When you use open-source OS's, there is going to be a trade-off. I am willing to accept that trade-off. I get security, no viruses or malware, FREE software, better OS efficiency, speed, etc. In return I am willing to give up native versions of a few things like games and iTunes. Most of the time I find that there are either native Linux alternatives or that I can run the apps in WINE.
The only software that I personally use that I can't use on Linux is Netflix's streaming movies. If you go to the Netflix forums, you will see tons of Linux fanboys like myself *****ing about their lack of Linux (and Mac) support. Now that Netflix is in the bed with M$ (the xbox 360 is offering Netflix), I am doubtful we will ever see them support Mac or Linux.
If you or anyone else don't want to make the trade-off, that's fine. Everyone should have choice (at least you know you have a choice since Linux and open-source is around).