My issue with planning poker (and estimates in general) is that there is still a social pressure to push your estimates down as far as possible and ignore reality. I still think deadlines and limiting scope is the way to go.
Within my teams, estimating doesn't appear to have downward pressure. Team members appear to want to estimate correctly because they want to have a realistic and steady workload. Driving down estimates means their workload goes up (at least in the short term, until our average velocity adjusts).