I did it at home, with a 5Mbps downlink that usually operates around 3.5-4 Mbps. It took over an hour to complete.
In comparison, I've downloaded the full 4.5GB Mountain Lion installer and that completed in under 4 hours.
Edit: just started a drivers' download right now at work. We have a blazing fast 1Gbps link thru Cogent, so any sluggishness will be entirely Apple's fault. Five minutes into the process, I see just about 20% advance on the progress bar and appears to be currently stalled, no movement at all. Will update when it finishes.