Over-The-Air iOS Software Update Saves 700MB of Downloading

iOS 5 Beta 4 is the first software update to be downloadable using Apple's new over-the-air updating system. As noted by @iam_lost, "iOS 5 beta 4 over-the-air update is a mere 133 MB, compared to the chunky 824 MB .ipsw file."

The over-the-air software update only downloads code that has changed or been updated in the update, thus making for a much smaller download. In this case, 691 MB smaller.