For example, there's no way to get a current version of iTunes running on Linux and while you can manage your iPod's music library with Banshee on Linux, you can't manage an iPod Touch or iPhone from Linux.
For these situations, if you don't want to give up Linux or switch machines, a virtual machine is your best answer. VirtualBox even has some support for Mac OS X now if you want to try to run Mac software and Linux side by side. Any virtualization program that runs on Linux though can run Windows XP and 7. I do that on a daily basis myself.
Put it all together, and, as you can see, there's little you can't run on Linux if you know what you're doing. Good luck!