Adobe CS3
I just installed the new Adobe Creative Suite 3, and I have to say, it really flies. This is the first Adobe release in ages where the apps actually got faster. And not just faster on my Intel MacBook, which would be expected from finally going Universal (more than a year later), but it's noticeably faster on my G5, too. For that alone, it's worth upgrading.
And also, while I originally hated the new icon set when I first saw it debuted as a big graphic several months ago, I am forced to admit than in context, they really work. The whole revised identity kit is terrific. And I appreciate that they have eliminated the needless overlap between Adobe and Flash apps, taking the best of both worlds and ensuring that they work in more-or-less the same fashion. Good work, all around.