I did competetive analysis at a previous company, and for someone who is good, it doesn't take long to scan a few forums and predict where a company may be going. A published (or even invitation only) roadmap makes things easier for customers and reduces some forum clutter.
Not all items need to be on a roadmap. We always had two versions available, public and private. Each containing what information we actually wanted publicly available.
Those who wont search, wont do it whether a roadmap is available or not.
Anyways, was just a thought. Certainly wont change my opinion of the company or product :)