i was annoyed earlier this month when I installed core2 test 1 and the update servers went down so that I could not update using yum. I didnt realize until I switched back to core1 that it was infact the update servers and not a problem with core2... a couple days later the servers were back up, but slow as hell.
That's one thing I really dont like about yum and apt-get. Thier dependence on a specific set of servers to be running smoothly.
know with apt I modified my set of servers to some lesser used ones to get better speeds (speeds with default apt-get from debian were closer to dialup than they were to cable).. with yum I haven't bothered to see if there are any mirrors or anything faster/more stable than the default.