I am the owner of the domain OSVISTA.COM. You would probably think "he must really like Windows Vista", followed by "how has Microsoft not sued him for that domain?" Thing is, I bought that domain years before Microsoft announced Vista; I just liked how it sounded. I use the domain for email, and I don't host any Windows related websites. Microsoft has never even contacted me about it, presumably because once they saw the registration date and that I am not using it in a way that conflicts with their trademark, they decided to leave me alone.
As long as you don't deliberately conflict with someone else's trademark, they have a very tough time arguing that they should be given the domain. Combine that with the fact that domain related cases are not heard through the regular court system, but under UDRP, and most companies won't bother.