If you're planning to install Mac OS X beta for day-to-day use, expect a dose of disorientation. The whole reason you're installing the beta is that you can't wait to live in the Aquafied world of Mac OS X, right? It ain't gonna happen. In fact, you'll probably spend most of your time in the Classic environment, which behaves pretty much like Mac OS 9. At best you'll get bounced back and forth a lot between Mac OS X proper and Classic. Few popular apps will be Carbonized -- rewritten to take advantage of X -- until well into the beta period. See www.versiontracker.com for a constantly updated list of Carbonized apps.
Here are a few pointers to help you survive the ride.
Basic Look and Feel When you're running a Mac OS X app, the menu bar looks Mac OS X-ish. No Apple menu on the left, no applications menu on the right, and so on. But when you're running Classic applications, the menu bar has the old familiar OS 9 look. It makes it hard to get used to anything.
Classic, the Application When you start up the Classic environment, you're actually running a Mac OS X application called Classic. If you click on the "9" in the Dock, you'll find yourself inside this application, wondering where the hell you are. Although it's called Classic, it has an OS X look and feel. Why is it there? It lets you Restart or Shut Down the Classic environment. There's a similar application, called Classic Support, within the Classic environment so it has an OS 9 look and feel.
Networking No matter how you have your network settings configured in Mac OS 9, when Classic starts up, Mac OS X will override them with its own settings. Location Manager in OS 9 gets confused by this OS X override and displays cryptic messages when you shut down. So you might as well turn it off. AirPort isn't supported in Mac OS X beta, so you might as well turn that off, too.
Fonts Mac OS X and the Classic environment don't share a common set of fonts. Your Classic apps will have access to all the fonts you had installed in Mac OS 9. But your Mac OS X apps won't, unless you also install them in the OS X Fonts folder (within the System: Library folder).
Extensions and Control Panels They're not accessible in Mac OS X, and they don't all work when you run a Classic app. In Classic, you'll probably want to turn off some extensions until they're taught how to behave properly under OS X.
Peripherals Printers, scanners, mice, and other peripheral devices communicate with your computer through bits of software known as drivers. Well, guess what? Mac OS 9 drivers don't work under Mac OS X. So peripherals need all-new drivers for X. Many of these won't be ready right away. Apple will provide some generic basic-functionality drivers, such as laser printers, for example, and for plain-vanilla mice and keyboards. But you'll probably have to wait awhile before you can use all of the features of all your peripherals with OS X. And printing to a USB printer from Classic simply doesn't work in the beta.
Don't Be Disheartened Just be aware that the OS 9 to OS X transition is going to be a bit rocky. As long as you're prepared for a bit of bizarre behavior, you'll do fine.