Sandyeggo - In the google webmasters help section under their "moving your site [google.com]" topic state
"We recommend that you move and redirect a section or directory first, and then test to make sure that your redirects are working correctly before moving all your content. "
I do agree with matt's for my store moving some products over and some not doesn't work or make sense. Google state's above it's more for text purposes so you don't 404 out your content. In their first 2 sentences of the topic it states help retain your rankings. Sadly it comes from google and if matt is saying different they need to reevaluate this their 301 topics..