Miranda Paul's blog post- A Peek at Pacing: 12 Picture Books I Love is a fun look at the pacing techniques used in 12 PBs. It's a great read. She also wrote about storyboarding if having something visual/tangible helps with the pacing process.
Diane Muldrow addressed the topic from an editor's viewpoint in Aug. 2011 on the SCBWI official conference blog.
Tara Lazar has a helpful post about picture book dummies and picture book construction.
I must admit that I have tried making dummies, marked page breaks in my manuscripts and read whatever I can find on pacing. I still don't know if I'm on the right track!