ergophobe - 12:02 am on May 1, 2010 (gmt 0)
Rosetta stone is not a brand, it's an archeological artifact first.
It *is* a brand, regardless of what prior uses may exist and it can still be trademarked, though it would be a 'weak' trademark. If I choose to use a common word as a trademark - think "Windows" or "Apple" for the two most obvious examples - I cannot trademark all use of that word.
I can, however, win a trademark infringement suit against someone who tries to sell and operating system called Windows, possibly even someone who tries to sell an OS called Doors.
You are right, though, a name like Windows or Rosetta Stone significantly complicates things when you're talking about using the name in "middle ground" cases where there might or might not be a trademark violation occurring.
And sometimes, filing a trademark suit can cause the problem to go away even if you don't have a legitmate case. Try to create a clothing item on CafePress that uses the word "caution" - they won't let you because some guy who loses every suit he files, has filed against them and it isn't worth it for them to fight it. Easier just to forbid your design.