Download copies from http://www.apple.com/support/manuals/. There are two manuals: a general users’ guide and a more involved “Designing Airport Extreme 802.11n Networks”.
I immediately jumped to the bits about setting up a remote USB disk, which seems like the feature I’d like to use the most. Didn’t see much about port forwarding.
Anyway, I haven’t had a chance to really go through anything in detail and it’s late and I need to go to bed. I just wanted to get the news out tonight so you eurofolk and eastcoasterian types could enjoy reading through the docs.