Agreed, 10.5 does not mean Aqua, Carbon, Cocoa, Quartz and Darwin are going to be scrapped. Classic support is probably finished, but other software seems to be pretty stable.
On the other hand, a new version means more bigger bloat for larger more powerful computers. Lots of gui extras that won't perform well on older machines.
On the other other hand, it's almost like they're officially fucking with Adobe. First, they kill Premiere with Final Cut. Then they switch to an architecture that Adobe can't/doesn't support. Now, right as Adobe is probably going into the finalizing stages of CS3, Apple announces a new OS, probably with new features an Adobe product should be taking advantage of. It's kinda funny to watch, as long as it doesn't get in the way of my workflow.