The only reason I can think of [right off the top of my head] to NOT register with the Feds is if you CAN`T register with the Feds or if you don`t care about your business reputation. For example, if your trademark is generic there is no good reason to waste your time and money. The down side to registering when you can is pretty small. Even when your mark is not in use in interstate commerce you can still file an application and let the business grow into it.
James Lindon, Ph.D. Patent Attorney
Lindon & Lindon, LLC
Patents, Trademarks, Copyrights, Pharmacy Law, Litigation
[this is not legal advice - provided for discussion only]
Intellectual Property for the Individual and Small Business: Identify, Protect, Enforce, Defend.
"Fools rush in where angels fear to tread."