I went to an interesting TAG (Technology Association of Georgia) Product Management breakfast meeting last week, and I participated in a buzz group that talked about Agile and Product Feature road maps. It was interesting that nearly every company/person in the session had the same experience about how to manage executive expectations.
Executives are focused on dates, much more so than features. Don't miss a date! But what you CAN do is get flexible with the feature set that releases on that date. Or if you like pithy rules: "Don't nudge dates; fudge features.
Now customers are a different thing, and they pay more attention to features. The collective wisdom of the group was to commit to only 80% of your capacity so you had some bandwidth to fix problems or accommodate late entries into the requirements mix. Some also had quarterly communications with customers to let them know what would be rolling out in the near future.
Another interesting nugget from one company was to let product managers communicate only with prototypes and not bullet points. It made sure that PM was talking about things on the "Do" list and not on the "wish" list.