Answer: When you are doing the Snow Leopard upgrade on your MacBook Pro.
To be fair, once the progress bar started to move it did take about 49 minutes, but it took about 60 minutes for the progress bar to start moving. 🙂
Once the upgrade was done I had to download about 650M of updates, which I assume are things that have changed since Snow Leopard was released.
It’s now all done and dusted. I’m hoping for an easy ride, but time will tell.