Sure, these are great resources:
Generally good advice:
Similar for 2007 and 2010 as for 2003 and 2007 or 2010
Basically, the overview is that your relationships will go into alert status after you migrate mailboxes and you fix them with the Recovery and Migration Management Tool Buy Now
Stop the Add2Exchange Service, migrate the users all at once or in a stepped fashion, Start Add2Exchange Service, those rels will go into alert and then you them with the Recovery and Migration tool. The tool is half off on support.