If you have "example" trademarked and you own the URL "example.com", there is minimal value in registering example.com as a trademark. The exception would be if you used .com as part of your trademark (and not simply as a web address to buy your goods/service).
I've got a brief jingle rolling around in my head where someone sings "hotwire.com". They are making the .com part of their consumer recognition. They should register "hotwire.com". I never see Apple advertise themselves as Apple.com, so they would not get any material benefit from that registration.
Also, keep in mind that someone else could register example as a trademark for goods/services unrelated to yours. Think of Delta Faucets and Delta Airlines, both of whom own Delta for their goods/services. A made up word, like Kodak, is going to receive broader protection, but it would probably be a mistake to think no one could ever use the same or a similar name for a completely different purpose.
Answered on Jan 23rd, 2014 at 8:22 AM