One of the more mysterious things that happens in MS CRM is the black magic that synchronizes contacts in CRM with a users contacts in Outlook.
Recently Kjell-Sverre provided a very detailed discussion on what happens when a contact is deleted – but it also explains a lot of the magic. The CRM team blogged a bit ago about how to clear the deletion tracking – it again gives more details that are interesting. You can read their post here.
One of the other great posts on the topic I found was the post on CRM to Outlook field mapping – You can find that here. We have an import tool that we created that among other input sources imports from Outlook and having some of this information would have been real useful early on!