Youch, I live in Seattle and anytime there is a large gathering of people, i.e. Bumbershoot, sports, there is very little chance of ATT data, 3G or Edge. Usually you can still get voice, but occasionally that fails as well. Also downtown in any of the big buildings has sporadic problems.
Now ATT seems to have this fixed in Austin TX... Of course public venues there seem to have higher probability of free WiFi which may take some of the burden.