I've just switched the beta server to send out a distribution of SiS that's much closer to the version we're going to be distributing on Steam. This means that 1.7gb worth of extra art will be downloaded by the updater, rather than being generated locally, as had been the case in prior installs.
I've temporarily upgraded our Amazon server to handle the extra load, but even so, the average download time will probably be around 30 minutes. It may be worth knowing that:
1) You can launch the game without triggering the updater by running with the commandline option -noupdate.
2) Partial downloads from the update server will be saved, and it should be safe to quit / restart the updater as needed.