Agreed. Without doubt OS X is an excellent platform. I just think Apple's change of direction towards "Form, then function" rather than "Form, and function" is depressing.
I think MacinTalk could use a bit more expressiveness.
Drag and drop sometimes works. It should work better though, because it should be handled at the object level, rather than the mouse-click level. Same applies to table rows; it should really be handled in the OS, rather than using clicking gestures.
Have you tried Adium? It might be a workable answer to Miranda for you.
Finally I do wish Terminal were better supported. I mean, reading the screen every time it scrolls--that's just daft, and unnecessary, and cuts off tons of useful apps that are only available from the CLI, like IF interpreters. It's great that there's Mudder, but isn't that really a failure case?