An analysis of iOS 5 OTA updates by innoying
blog.innoying.com
blog.innoying.com
Well, I'm not sure it makes a difference. As he later points out, update packages are signed by Apple, so unless you have access to Apple's private key you can't make an update package that will actually be installed.
Using HTTPS instead of HTTP would be wise, but in the end it doesn't make a difference.
On the whole though, this is a fascinating exercise. Thanks!