I have been trying to restore my iPhone 4S over iCloud since yesterday. Invariably, it will fail with the message that the iPhone is no longer connected to the internet.
The wifi over which my iPhone is connected is also being used by four other computers that have no problems maintaining their connection with the internet.
Currently, the estimated time remaining for the restore is 11 hours. It has come down from 52 hours. This over a broadband connection of 120Mb/sec down and 9 Mb/sec up.
The size of the backup on iCloud from which I am trying to restore my iPhone is 8GB.
Edit - to clarify: the problem is that iCloud restore fails. Also, I tried turning off my Airport Extreme router for about five minutes earlier today. No luck: restore from iCloud failed after an hour and a half with the message that the iPhone was not connected to the internet. I also tried to connect the ADSL modem directly to my MacBook Air, sharing its internet connection over wifi my my iPhone 4S with the exact same result.
Edit 2 - I can start the restore, but it finishes after an hour or so with the dialog box that the iPhone is not connected to the internet.