How long does a clean install of Lion take?
About 40 minutes or so. I'm assuming a 5400RPM drive, 7200RPM or an SSD would be faster, obviously.
Macbook Pro i7 2.66GHz - USB install (copy image to USB, not install via Snow Leopard).
1st part (downloading additional components) : ~8 minutes
2nd part (actual install) : ~18 minutes