Start reading the thread for “Default buttons, focus stealing applications, and User Interface Continuations.”
here.

There are a lot of good points. I just want to comment on the paper (PDF) Richard linked to about UI Continuations. We just have to remember that often, perceived UI “improvements” sometimes comes with a price and the price I see is complexity. The example sited of a person wanting to lookup multiple e-mail addresses at once and the desire to maintain multiple name-browsing contexts begins to make get muddled in my mind. I’m not even sure I can describe the point sufficiently using words alone. I don’t see a novice user benefiting from this “improvement”. Some will always prefer a single-task wizard-like approach.