An extremely cautionary tale on broken iMacs, Apple's relative indifference, and how barbaric this all seems in relation to hardware from other vendors:
Long story short, I'm setting up a shiny, new iMac with OS X 10.7 (aka Lion) for my graphic artist mother whose 2003-era G5 decided to die catastrophically and quickly.
Once I figured out the ancient SpeedStream modem's PPPoE issues with her formerly SBC, currently AT&T DSL connection, got her Ethernet-equipped HP LaserJet 4000n printer on the same network as the iMac (once I figured out the printer's IP address through printer-top button-pressing voodoo), all that remained was bringing the HP Scanjet 6300c scanner to life.
It shows up in the detailed view of "About this Mac." But no software is automatically downloaded (that's how OS X 10.7 configures printers and scanners, apparently, and it dealt with the LaserJet 4000n that way).
The USB-connected scanner appears to be dead. To OS X 10.7 anyway.