I wouldnt doubt that their servers are busy. The news didnt break that the ICS update was ready till Tuesday. Most people were at work when it hit. So starting Tuesday night and since people have been hammering the Samsung Servers to get the Drivers, Update and Kies.
So yeah it might take a day or to. No this is not the first time this has happened with a major release. I know that Apple Servers have been slowed on release days of new versions of iOS as well as Microsoft Servers when they release a new Preview of their upcoming OS. It happens, no way you can account for all the people that will download the update. Their servers can handle normal traffic but not the influx of traffic that this update has brought.