The worst problem with Munich's Oktoberfest is not related to the beer or drinking too much of it (at least not from my perspective, with being able to properly and responsibly consume Augustiner), but rather having to deal with O2 Germany, the European tele-communications company...
Who would have guessed that during an event, where many foreign visitors are attempting to get temporary internet access, a technology based on a shared medium would get somewhat slow?
Not trying to defend O2, but unfortunately I doubt you'll have a better experience with the competitors during oktoberfest. They're not very inclined to extend their network for a temporary load peak.
Next year, maybe try to get a hotel with free wireless?
Most networks struggle in Edinburgh during festival time, I also think your dongle should work under linux using network-manager in conjunction with modem-manager, I've got a few lying round the house including the old PCMCIA cards too
That tends to happen at crowded events. I went to Washington DC once for an event, and I was probably the only person there with AT&T because everyone else had Verizon and couldn't even get a voice/sms connection let alone 3g, and then there was me with 5 bars the whole day.