One thing that can cause localised problems is Akamai. I don't think Google or idg use them though. But I went through a period where sites would seemingly go down. I checked the activity window, and it was always a static resource on an Akamai server that had timed out. It's a weird problem until you realise it, because it means that big sites go down a lot more frequently than small ones.

That probably isn't the cause of your situation, but maybe in the activity window there's something that'll give you more info to help diagnose the problem. You might even want to try a packet sniffer or something.

Oh, and as I write this runrev.com is down for me.