Microsoft says the demand for Windows Vista Beta 2 has been huge. They have hit the ceilings on bandwidth and are serving out product keys ten times faster than they can serve the downloads.
They claim they are pumping out the bits as fast as they can, if they pushed them any faster there would be a measurable impact for the Internet:
We are pumping out bits as fast as we can. If we pushed out bits any faster there would be a measurable impact for the Internet. So, we are literally saying that if we increased our bandwidth any further there's a possibility of taking down the Internet - people might have problems with World Cup viewing, etc. That would be bad. So, it isn't that we weren't anticipating demand - we were and are - it is that we are at the threshold of what the Internet can bear.