crewmeal,
Apple run most of their high-volume systems over CDNs (Content Distribution Networks). So it may not necessarily be an Apple issue as such, but an issue with one of the CDNs (e.g. Akamai).
Furthermore, due to the heavily localised nature of CDNs, some people may not be affected at all. For example, I was doing some updates a couple of hours ago and had no issues authenticating or downloading in iTunes.
The downside is that if it is a localised CDN issue affecting only certain geographies, then it is a little harder to diagnose and track-down the root cause.
In a nutshell, I guess I'm saying give them an hour or so and it should all be back to normal.