Here's an interesting list of applications supposedly killed by Leopard. There's no question that there's a huge amount of functionality in Leopard that was taken care of in Tiger by third-party apps (and this is just a list of freeware-- commenters pointed out last week that Jisho was made almost obsolete by the Japanese dictionary included with Leopard), but I'm not so sure this list is all it promises to be. No amount of tweaking to Spotlight will ever replace Quicksilver, and as good as iChat has gotten, I still like Adium for its easy customization.
And apps like CenterStage, who used to have a one goal (an open source Front Row replacement), have now been able to spread out and become more their own program instead of worrying about Apple's missing functionality.
As always, the best app for the job depends on both the job and the person doing it, so there are probably more than a few places where Leopard stepped up to fill functionality that users used to trust third-party software for. But it's a stretch at least to say Leopard killed these apps-- replication of one function now built into the OS doesn't mean all the apps other functions are useless.
[Via Fake Steve]