I have to add my voice to the crowd of folks who were not having any problems before but are completely unable to play now. That's Skirmishes, Custom games, Pantheon, nothing over the 'net. The only thing that works here now is local LAN play. The problem that I suspect is that we are three players in the same household using one Internet connection. Here are the details:
Three high-end gaming rigs, one running XP Pro fully patched and SP'd, two running Vista Ultimate, again fully patched. We are using a Linksys BEFSR81 router with firmware 2.51.3. When I check the router I see that it has automatically set up port forwarding (I never touched it) on the following ports:
6100-6200 and 6073-6074, Both UDP and TCP
Note: we have 3 Xbox Elites in the house and play a lot of console games, too. The XBox has a Network Connection routine that will check your router and "rate" your router's NAT settings compatibility according to three ratings: "Strict", "Moderate" and "Open". They have a list of conforming routers on their web site that will provide "Open" NAT settings and warn that anything less may lead to connection problems. I specifically hunted down this router because it is on Microsoft's compatibility list and when we use it and run Microsoft's test, all 3 of us get an "Open" rating. We have great XBox gaming (currently loving Sacred II, by the way).
When any one of us plays a Custom game or Skirmish, we can join games fine (subject to whatever problems any of the other players have). If the three of us (who all bought a copy) try to create a 3x3 custom game, for example, it tanks. We get set up reasonably ok in the lobby with the usual waiting and watching people try to connect, but once we're set up and launch the game there is an inordinate delay for 2-3 minutes, after which we inevitably hear the "A Player has left the Game" annoucnement and someone has turned into an AI. Usually it's one of us and the one of us that got booted is now playing against all AI in her own game, while the rest of us in our game are connected fine (including my son and I), while my wife's player has been substituted with an AI. This is both with and without the proxy switch on the command line. With the switch, of course, the pings go up into the 250-300 range (I imagine because the connection is being routed through your midwest offices).
We play zillions of online multiplayer games, that's all we ever play. Including other P2P and client/server games. We've played D2 for years, Titan Quest, Sacred, and this is the only game in which we are experiencing any of these problems.
Hope that helps. And I hope you can get over this. I'm a little surprised and disappointed that you gave everyone the Memorial Day weekend off, when so many of your new users are going to try this out. When I was running a software company I don't think a single programmer on our team would have wanted to leave their code in this state, they would have stayed until this was working. This is make or break time for your game, the word on the street is already "Great game, sucks over the Internet". That's like a failed MMO launch, you only get one chance, so I really question the time-off call. Well, good luck whatever happens.
There's always Sacred II on the XBox (did I mention what a cool game that is)?