I am quite interested in this area, I have some questions.
@rogerd, can you see the old pages spidered? I.e. has 301 been discovered and page still not dropped from the index or is it the question of Google crawling old pages and finding 301 but still holding to the page in its index? Also, if they are both in index, which one is ranking more prominently, the new or the old 301-ed page (or better - can you see 301-ed page only with the site: command?)
@tedster, the same question with regards to spidering, from what you wrote above I am presuming you are seeing both, new and old URLs in regular SERPs? Are old 301-ed pages ranking better than new ones or is it a mix?
I am also wondering if with a brand new site Google is even slower to drop 301-ed URLs - almost like "This is a new site, I am not sure if this is what you really want or are you still messing around with URLs.."
I have noticed that in the last 6 months or so (perhaps something to do with Caffeine going live), the whole process of dropping redirected URLs is longer than before. It is almost as "we have a capacity so we can now hold onto the stuff in index longer."
I could be wrong but this is my observation.