Ask Slashdot: IT Staff Handovers -- How To Take Over From an Outgoing Sys Admin?

Solar1ze writes "I've just started a role in an IT services firm. I'm required to take over from an incumbent who has been in the position for three years. What are some of the best practices for knowledge transfer you have used when you've taken over from another IT staff member? How do you digest the thousands of hosts, networks and associated software systems in a week, especially when some documentation exists, but much of it is still in the mind of the former worker?"