There are lots of problems with brainstorms, but the main one is they don't go on for long enough.
They usually stop when people have run out of ideas and you get those embarrassing silences. But those embarrassing silences are when your unconscious starts engaging on the problem and is a vital part to coming up with great ideas.
The way brainstorms are practised in most companies today is still almost exactly the same way that was recommended by their inventor, advertising executive Alex Osborn. But he invented it in 1953, over sixty years ago. Business and our understanding of how the brain works has moved on so much in that time and yet we're still hanging onto this old technique for so many of our idea gathering sessions.
The fact is, brainstorms do have a useful part to play in solving problems. They can be very useful at the start and the end of the process. The trouble is a lot of the time they're used as the only part of the process.
Here are some of the problems with a brainstorm: