I know this is a long shot, but I figured I'd try...
I have periodic network connectivity glitches. I'm not sure what's causing them. Every minute or so the internet is inaccessible for 2-3 seconds. I'm not sure if this is actually a complete outage or just temporary extreme packet loss.
Here's an image of the Source net_graph (lower right hand corner) during the glitch while playing Counter-Strike:
The dense parts of the graph are normal. The parts where there are many frames of 0 bandwidth punctuated by huge packets are the glitch. You can see that the "choke" (update packets per second that recently haven't reached the client - this should be 0) is huge.
Does anybody, I don't know, recognize that kind of problem just by looking at the graph?