I'm not sure if this is a 3.0-specific problem or not, though I never saw the behavior prior to 3.0.
Sometimes (not always) when I load my app, the whole thing fails to load and I get a white screen. If I click in the lower-left hand corner of IE I get an error message that 'esri' is undefined, leading me to think the call to load the API did not succeed properly (just a hunch though).
Was anything changed in terms of how the API loads itself when called between 2.8 and 3.0?
Sadly I can't access our app using Firefox due to corporate security restrictions but I do have access to Fiddler, if that will help someone identify the issue.