With the iMac I personally don't like the glossy only screen, but that's just a preference thing, plus I'm not a fan of all in one systems.
But as for your question on OSX/Windows/Linux, it's as easy as pie, just install Fusion and you can have all three running at the same time
Bootcamp will also do windows perfectly, but for booting into Linux without VmWare it's a little tricker, but doable (I just can't remember how).
As for apps, all the platforms have what most people need I guess, some are more suited for certain things, and some platforms have gaps in what decent software is available, as much as I prefer the mac OS I have to maintain a certain amount of OS agnosticism to do my job, and game