I definitely set unrealistic expectations for my customers, as identified below. In the past I've been bad about overpromising and then spreading our dev resources thin, which definitely contributes to this feeling that customers are pushy (because they don't get what we've promised).
This is something I've gotten better at recently, but still remains a major pain point: Keeping customers happy with the CURRENT featureset rather than promising new things.
I would say it's one of my greatest weaknesses.