If you have established use of a mark before the registration (or use) of a competing/conflicting mark, you can defend it.
In fact, registration arguably provides no protection other than the fact that it makes it easier to search for your mark in the USPTO registry.
Isn't the trademark legally yours if you register and no one challenges for some period of time (I want to say 7 years)?
Massive corporate behemoths have lost local TM use because some mom-and-pop store was using a trademark first.
[0]: http://en.wikipedia.org/wiki/Waffle_house#Waffle_.26_Steak
http://en.wikipedia.org/wiki/Hungry_Jack's#History_of_.22Bur...
"When Burger King moved to expand its operations into Australia, it found that its business name was already trademarked by a takeaway food shop in Adelaide. As a result, Burger King provided the Australian franchisee, Jack Cowin, with a list of possible alternative names derived from pre-existing trademarks already registered by Burger King and its then corporate parent Pillsbury that could be used to name the Australian restaurants. Cowin selected the "Hungry Jack" brand name, one of Pillsbury's U.S. pancake mixture products..."
The court ruled that federal trademark registration had priority over state law, and that the big chain Burger King had rights to the “Burger King” name everywhere except in Mattoon, Illinois. Since the Hoots family had prior actual use there, they retained the name for the Mattoon area.