"The courts read any failure to protect your trademark as good reason for the courts to not help you protect it later when you find the infringement significant. As the trademark attorney in the clip noted, Elevator, Thermos, Aspirin, and Trampoline all lost their rights to their trademarks, because they didn't "police" their trademarks."
From: http://stosselintheclassroom.org/video_activityMar08.html
(Important for startups:
http://blog.startupipservices.com/archives/top-startup-trade...
I'm sure you knew already, but it doesn't hurt to reinforce the importance of trademarks.)
Edit: dotBen made a similar point further down the thread
So what is the downside in this scenario? How is Bayer hurt by not owning an Aspirin trademark any longer?
The answer is Kleenex. Now try to tell someone in a general conversation that you when you're talking about Kleenex, you meant 1) the actual company Kleenex, not the 2) product nor the 3) other generic tissue paper products. Because now you have to explain to consumers why your Kleenex is better than your competitors Kleenex, when before you could just say 'Kleenex, the brand that works' or 'Kleenex, the brand you trust' or just plain 'Kleenex'. Even if it's just a name, if you reduce the number of ways for you to differentiate your product from others, it just makes it harder to do so.
It seems silly now, but to many of these companies, it's the way for them to be unique, to stand out among the crowd. Because they came up with the word 'realtor' and 'entreprenur' to describe themselves, not to describe others. And, rightly or wrongly in this case, the government said that the words they use to describe themselves was so unique that it was worth it to legally make it theirs.
(And all the past successes of these names being turned into generic terms (Kleenex, Xerox, Aspirin) is the other reason why these companies are fighting tooth and nail to make sure it doesn't happen to them. The government has basically stated that it's a use it or lose it situation. And they are determined not to lose it. Whether or not that's a good thing....)
I think the only times I've ever said "realtor" has been when it was informal. Having researched the NAR, MLS, etc. before selling my house, it seemed fairly obvious that realtor was a trade name and something I just assumed was trademarked.
This is why it's ok to use the word "entrepreneur" in general, but not as the name of a magazine or "communication product".