I'm guessing US laws could be a little different, but basicly if you use the site activily (and not just as mail-addy) you are a lot more secure in your right to the name. Of course usually when buying a domain you also sign that you aren't violating 3rd persons rights in doing so - so its always a greyzone. Personally I got bullied (read lawyers) out of a domain some years ago, but I didn't use it activily - I was only working on a site to place there and had been for years (yep, more important things kept popping up), I won the right to the domain in the first (and free) "battle", but then they dragged me to court - and I couldn't afford to not win (and you never know in courts) so we made a compromise and the bought me out.