I thought there was something about where if we're legitimately using the name, then even if we don't file the trademark, no one can come along after us and file for it... am I wrong?
However, be aware that everything I know about trademarks I learned over the an intense 6 week period when Sun was trying to figure out what to call Java (my suggestion was 'Silk' :-) and the browser (initially WebRunner but that was already in process by Apple/Taligent).
Do consult a lawyer, do file for a mark if you want to keep it.