This article is from the Macintosh for sale FAQ, by Elliotte Rusty Harold firstname.lastname@example.org with numerous contributions by others.
I've never heard of a delivery taking more than a year, and
most Macs ordered through whatever channels arrive within six
months. However I strongly recommend not putting more than a one
dollar deposit on any Mac purchase and making certain that you can
back out of a purchase at any time up until the goods are actually
delivered and signed for. It's not uncommon for Apple to lower
prices or deliver an improved model at lower cost before all orders
for older models have been filled. This is especially common for
orders placed through the educational channel. For hot models like
the PowerMac 8500/120 you may want to place orders at several dealers
to have a reasonable chance of getting what you want when you want it.