Did you know you can print envelopes directly from Address Book in 10.4? According to the Address Book help, this is a new feature. I know I haven't seen it before.
While viewing an Address Book card, or while multiple cards are selected, choose the menu item File -> Print. In the Print dialog, there are options for printing lists of addresses, mailing labels, pocket-sized lists, and ... envelopes. Lots of different sizes and shapes are supported.
For more information, search for "adrbk1562" in the Help Viewer application.
[robg adds: I know this is a pretty basic hint and it's just one regarding a new feature, but I asked a few iChat buddies about it, and a surprisingly high percentage didn't realize that envelope printing support had been added in 10.4 ... so now there's no excuse not to know!]

