Let's be realistic... why in the world would they invest in beefing up their servers 100-fold to accommodate the millions of people trying to update their software on one single day? Doesn't make any sense AT ALL. Be patient, it'll download when traffic slows down.
*Sheesh
If the servers aren't expected to serve unfettered demand then Apple should stagger the demand.
Why not release the iPad update today, iPhone 4 tomorrow and iPhone 3GS the day after? Why not throttle the number of devices being told an "Update is available" rather than letting it fail part way through? There are many ways of managing this that don't involve people sitting in front of their computers getting frustrated.
What's currently happening is ugly, the error messages are scary and I've seen at least one device that needed a recovery. Hardly an auspicious launch to iCloud.