From a sales perspective, roadmap presentations are the anti-sales pitch:  a well organized presentation of all the things your products don’t do.  Great, let’s spend lots of time talking about that.

From a competitive perspective, you’re broadcasting your plans.  If you’re presenting roadmap to every prospect who comes through the briefing center and at every local user group meeting, your competition is going to learn your roadmap, and fast.  Then they can copy it and/or blunt it.

But what irks me the most is what happens from a product management perspective:  you turn PM into “the talking guys” instead of “the listening guys.”  Given enough time, PM starts to view itself as the folks who show up and pitch roadmaps.