Kahney argues that the "new" virtual keyboard and Exposé in the Dock are signs of preparation for an Apple tablet:
The more I play with Snow Leopard, the more it looks like it's designed to run Apple's upcoming tablet.
However, there are simpler explanations than these conspiracy theories (without even entering into the debate of iPhone OS—the most likely candidate for a 10-inch tablet—vs Mac OS X. Clumsy desktop operating systems don't translate well to slates, as Windows has demonstrated many times).
The virtual keyboard has been in Mac OS X forever as part of the input system. In fact, it was part of the old Mac OS as well, and was incorporated as part of the input menu system in Mac OS X. In Snow Leopard, you can activate it using the Keyboard panel in System Preferences. Go there and check "Show Keyboard & Character Viewer in menu bar".
Before, the keyboard window used to be so tiny—as you can see in the top image—that it even made people whine about it in Apple support forums. Fortunately, Apple changed this and now you can resize the window as much as you want.
There's no magic here. It's just a vector-based app that can be scaled at any size you want. The same happens with the Character Viewer.
So, if this is not a sign of the tablet, what could it be? Apple has been working on a fully resolution independent display model since Mac OS X 10.4. During every Worldwide Developers Conference, Apple has been preparing developers to ready their apps for the jump. Mac OS X 10.5 Leopard implemented a system wide resolution independent model (unfortunately, it was systemwide and not on a per-screen basis).
The objective: To be able to use ultra-dense resolution displays without making everything on the screen tiny. As a user, if Apple decided to turn on this feature, you would see that menus, icons and buttons use the same physical space no matter what display you use. Things would have the same size but would look sharper on a display with more pixels per inch. Example: A button will be one inch wide in a 24-inch 1080 pixel-wide display and a 24-inch 2160 pixel-wide display. However, it will look a lot sharper on the 2160 pixel-wide display because it will be made of more dots.
If you have the developer tools installed in your Mac, you can check the scalability of the user interface using Quartz Debug. This tool allows you to zoom in and out of the user interface, seeing how everything—except bitmap elements—scales in real time, with no pixelation.
What about Exposé on the Dock? I'm a believer in Occam's razor theory: the simpler theory is always the better. In this case, Exposé on the Dock is just a more convenient way to see your open application's windows. More intuitive and easier to use for the normal user than hot corners or function keys.
Bottom line: I've no doubt that touch interfaces will come to Apple devices, but these two functions are not any indication of it.