Scrum Reading: Estimating

I’m a big fan of Mike Cohn’s books and recently attended his Certified ScrumMaster training in Boulder.  I love Agile Estimating and Planning and have taken a lot of useful information from his Planning Poker approach to estimating.

In working with clients, I’ve found that estimating is still the hardest aspect for developers to get a handle on.  Has anyone used planning poker in estimating or are there other methods that you found to be more successful?

Would love to hear from the rest of the group as to what you see working and what’s not quite getting you the results you need.