What is new is compatibility with Snow Leopard (mostly -- some plugins are still lagging behind), and a host of background changes. Clang is being used as the default compiler, which the change notes say should speed up runtime significantly. Localization has been tweaked, and lots of previously buggy actions (mouse tracking on triggers, for one) have supposedly been smoothed out and improved. Not necessarily a marquee release, but at this point, any Quicksilver release is a good one.
And if you've never actually used Quicksilver, well, now's a great time to start. Ostensibly, it's a app/file launcher, but the more you learn and use it, the more it becomes a "connector" for everything on your Mac. Your mind is connected to your fingers, and your fingers connect to the keyboard to invoke Quicksilver, but Quicksilver is connected to everything else.