If you want to avoid the flickering, you could follow Joel's advice: "Don't hide or disable menu items" and when a user presses a toolbar button for something already executing or that would interfere with another executing task, you can then either show a message on why you can't complete the users request or "cache submitted tasks" (and have a window of tasks to be executed) or just do as the user requests and execute it again (be aware of synchronisations problems here).

Disabled buttons while long running task
I've decided to check this site out since it was tweeted by the great Jeff Atwood himself. The first question I saw was "Advice on making ruby code more ruby-like", which is the kind of question I see all the time on Stack Overflow.

So what is the difference between the questions on SO and the questions here? It seems to me there is enough overlap between the two that the difference is not clear, and I may not be alone in feeling this.  So far this site seems redundant.
