This post from Carl Franklin couldn’t be more on the money in my opinion. I have found the domineering window issue to be a major annoyance in the past and present.
While I haven’t published my credit card number to the world yet, I have experienced a few “Phew! That was close” moments jumping between financial reports, proposals, IM conversations and secure forms at the same time. Yah I know the perfect user isn’t supposed to do multiple tasks like that at once but reality often dictates otherwise.