Often I send a document to the print queue before I have access or am connected to a printer, so I can close it and be done with it. However, sometimes I forget to print and then shutdown without printing. This is quite obviously a pain as you have to start up again, log back in, and open the print queue.
And so it would turn out Mac OS X (10.6) has got our backs here. If you shutdown your computer with an item still in the print queue, and then connect your printer (I've only tried this via USB so wireless may or may not work), then startup your computer again, at the login screen, before even logging in or doing anything, your document will print automatically.
[crarko adds: I think I've done this with networked printers as well, maybe ethernet only. As long the printer becomes available before the queue times out, things will behave normally.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2011110213314638