Brainstorming has to be efficient as well as executable. It is indeed a great activity which brings out the best ideas, but without the right outputs, the exercise can be nothing less than frustration.
Brainstorming can be great only if the person which is driving is very clear of the outcomes of the discussion. There needs to be clear to-do tasks as soon as a conclusion is reached. A brainstorming session which is not properly charted, will be a mess. If you are able to focus on these things, you are very well on track.