I was wondering the same thing too but yesterday, I called RIM's Playbook Technical support line and I was told that for some unclear reason, you aren't able to make folders directly in the Playbook's main directory when it's connected to the computer. However, I was told that you could only make folders within the folders that already existed when you got your BlackBerry Playbook. Hope this helped answer your question.
In OS 2 you can make new folders by dragging icons from the tray on to one another. I believe this function hasn't been implemented in OS 1 for some reason. Alas, hopefully only one more month until the updated OS comes out of beta.
Until OS2, you have to make use of the provided tabs. Once it is released, you'll be able to make folders for icons. It also has a launch bar and multiple panes of icons if needed. Putting folders on the luanch bar works great for me.
If you need to create folders for files, you can do that with the free AIR Browser app, but you are limited to subfolders of the existing ones.
Hopefully OS 2.0 will be available for all Playbook owners on time. Aside from that, there are several apps that RIM had made that are currently only available on the smartphone side such as the Windows Live Messenger app and the Twitter for BlackBerry app that I hope RIM would consider bringing to the BlackBerry Playbook.
You download the FREE Air Browser from Appworld and it allows you to create folders. Or you can create them using usb or wifi-sharing and Explorer.
Other than the photo/pictures app, folders only serve your own organizing needs as they are ignored by most apps. The Picture app will present folders under it as separate Albums for viewing pleasure.
