[RiderOfGiraffes]

Clickable: http://en.wikipedia.org/wiki/Planning_poker

With regards helping people make their estimates better, make them visible. What gets measured gets managed, and people can't improve unless they can see the target. Make a note of their estimate, and compare against the time it actually took.

You can make this "public" within the company, or you can keep it between just a few people, but you must make it visible. Most people will self-correct when given the data.