they must have massive bandwidth set up now, I just pulled in the whole 803mb 5.1 install for my phone very quickly. Historically that has been a problem on release day.
The last update, as well as this one, seem to be "akamaized". The 5.0 update was horrid, after an hour I gave up and tried the next day. Today, the 5.1 update is going along between 5 and 10Mbps (about half what it could be going on my connection, but I'm not complaining).
Akamai puts their servers on ISP owned/operated networks. So Akamai manages the content, and can steer users to one serer or the other, but the ISPs are in complete control of the network serving those machines and any congestion. My guess is that Akamai got an earful from Apple over the 5.0 release and made distribution/steering improvements or providers using Akamai realized that a 100Mbps (or less) connection to their akamai servers was not sufficient and provisioned the servers for the full 1Gbps (or more). Another possibility is that there simply isn't the same mad rush of people trying to download IOS 5.1 all at the same time.
btw, we have had several Akamai servers on our networks and the latest ones we had came standard with several gig-e ports. Akamai required at least a 100Mbps full duplex connection before they would even activate the server for content distribution (although through the magic of QoS policies, network design, etc the server might not actually be able to make use of that). The last published figure I saw on Akamai is that they have > 100k servers. If you estimate half are provisioned with 100Mbps and the other half are 1000Mpbs, that's 550,000,000Mbps (550Tbps) of combined bandwidth to the eyeballs of the world.
