We have started getting more and more questions (as well as some support cases) around Address List Segregation with Exchange 2010. Some of our customers have also assumed that the existing Exchange 2007 documentation on the subject would just apply to Exchange 2010 also and have tried to configure this, usually with bad results.
Dave Goldman - one of people who worked on the Exchange 2007 document - has just posted a blog post detailing the status of the existing document and it's use with Exchange 2010. In short: DON'T DO IT. There is a new document in works for Exchange 2010 and we will definitely let you know when it releases, but trying to apply Exchange 2007 document to Exchange 2010 leads to Bad Things.