There has been a lot of news lately about lawsuits and legal cases where owners of domain names are being asked to surrender their domain names to companies that own the trademark of the same name. A very simple example would be if you bought the domain name "xyz.com" and a company already owns a trademark for the name "xyz". If the company that owns the trademark is defending its trademark... it will have no choice but to ask you to "Cease and Desist" the use of that domain. In fact, they will probably ask you to surrender the domain name to them!
Based on discussions with other domain owners who have faced this issue... most were able to "sell" the domain to the company as it was probably less expensive for the company to buy the domain quickly rather than spend the legal costs to take it (not the mention the time saved). But, this is not always the case... depending on the company, they may want to make an example and demonstrate they will defend their trademark no matter what the cost. In this case, you will most likely have to surrender the domain name or face a legal battle.
Regardless, there are ways to avoid this from happening. When you find a great domain name and want to purchase it... take a few minutes and do a search for existing trademarks. Here is one place to start this search: http://www.uspto.gov/main/search.html (Click the "Trademarks" link on the left to search). Based on the results from these search options you will at least have done a basic search for US trademarks and registrations. To go beyond this level of search, you would need to contact a trademark attorney for assistance... which can run anywhere from $99 - $399 depending on how comprehensive the search will be.
For me, I try to perform a basic search if I feel the domain name might have a trademark issue. Beyond that, I simply use my best judgment before registering a questionable name. I just can't imagine buying a domain name and then having it taken from me because there was an existing trademark.
Finally, a different kind of caution is worth mentioning... there are scam artists out there that will pose as companies that own a trademark and ask you to transfer/sign over your domain name... when in fact, they are just trying to "steal" your good domain name. Be careful of this scam... and make sure you are dealing with a reputable company and an actual registered trademark before transferring your domain name to anyone!
So, be a little cautious and keep searching! Ron