PersonalBrain is an excellent application, but has a few faults. To adequately describe PersonalBrain would take more space than I have here, and there is no need to, because the developer provides wonderful videos and screencasts. Essentially, the application allows you to drill down to any level of detail in your information and still see the bigger picture, and it does so far more effectively than any other piece of software I've used... and I've used a lot of them.
I also like the fact that I can run PersonalBrain on my PC at work and on my MacBook at home, sharing some of the same databases via Dropbox.
I do wish PersonalBrain had a more robust note editor. Right now it is really only useful for jotting simple notes, not composing long text. But you can associate RTF documents with your PersonalBrain items, and quickly open those in your favorite word processor. Copies can be stored internally or externally, and are fully searchable.
In short, PersonalBrain is a well thought out information manager with a unique and very powerful user interface.