Everyone in the domain business should read the book "Trademarks: How to Name Your Business and Product" from Nolo Press
http://www.nolo.com .
United Airlines, United Van Lines, United Fruit. Multiple companies sharing a trade name used to be common. I wont go into everything covered by the book, but everyone here should buy and read the book. It is outstanding. I used it to get a Federal registration on hiOsilver , the name of my company.
http://www.hiosilver.com
If you use a non-obvious but trademarked domain for a legitimate purpose, you have little to worry about. The most you are likely to lose is the name, and that is not likely. The longer you use a name, and the more alternative domains for the TM holder, the less likely they will bother with you. In general, lawyers cost a lot and only really valuable names are worth reverse-hijacking by TM holders.
I sold TampaBayMagazine.com to Tampa Bay Magazine for a modest sum, and they were happy to deal with me. When I regged it, I did not know of the magazine. I had a real purpose in regging it, but never got around to using it. The magazine owner was a lawyer, so he knew it was better to buy from me than hire a TM lawyer. You do have to be careful about how you handle these situations. It is best if you can get them to make an offer, rather than you naming a price.