So what does this tell us about 10.5 and its impact on the Mac, both for developers and users? Sounds to me like there are some pretty ground-breaking changes in Leopard since, from what I understand, developers typically try to keep theirs doors as open as possible by maintaining backwards compatibility with at least one previous version of the Mac OS. Of course, this can vary depending on how difficult it is to keep these doors open, as well as whether the developer works out of an office or a living room.
Personally, this boosts my excitement for Leopard. If it changes things as much as developers keep hinting, 10.5 sounds like it'll be a fun ride.