Apple has told us from the start that Snow Leopard is predominantly about streamlining both the size and speed of the operating system. Installing Snow Leopard should take about half the time of performing a Mac OS X 10.5 Leopard install, and it's expected that you'll gain about 7 GB of space back on your hard disk.
Snow Leopard is also bringing some new features to the table, including 64-bit support, Grand Central Dispatch's multicore support, and OpenCL, all of which can provide better performance for applications. There are amazing improvements to the Mac OS X Universal Access features, particularly for the vision-impaired. For those who use their Macs in a predominantly Windows office environment, the full built-in support for Exchange should make life much simpler.
TUAW would like to know what Snow Leopard feature you're anticipating the most, so we've come up with a short list for you to choose from in a poll. We'll use these results to provide you with detailed coverage about those features. If your favorite improvement or feature isn't on the list, leave a comment and tell us what you're excited about.