It is hard to explain, but easy to understand once you work with it. A brain consists of all of the knowledge you want easy access to on your computer. You set up areas of focus (Business, Personal) and then sub-topics or departments (Sales, Marketing, Shopping) and so on, going down in a reverse-tree fashion.
I imagine this would work well in an organization or someone who sees things more intuitively than I do. For me, it involves too many steps. If I need to find information on a client, Ed Jones, I go to Business->Clients->Ed Jones->Projects->Project with Info... you get the picture. It makes sense when dealing with huge amounts of information, but for a small or medium business with file systems already in place, the cost to implement might be more than it is worth.
Where this would work best is on websites. I didn't try WebBrain, but it would make navigating a large website much easier. While TheBrain uses Brain navigation on their site, I'd prefer to see it in a popup window or something other than frames - it makes it difficult to link to information within their website.
