It also relies on Quicktime 7 (for h.264), which I am sure will be released concurrently with 10.4.

There is some noise being made at the moment about the fact that Quicktime 6 pro users will have to buy a new licence for Quicktime 7 Pro if they upgrade to Tiger. Second hand from macfixit :

Not much different from upgrading from QT 5 to QT 6



Yep - and I'm happy to pay, but what people were complaining about was that they didn't realise that installing Tiger would mean that they have to upgrade their Quicktime Pro. Tiger 'breaks' Quicktime Pro 6.

I'm not positive this is true, its just something I've been reading on FCP boards. Like Rod says, it's likely to be bundled with FCP 5, but if you aren't buying FCP then you might want to check into this if you use Quicktime Pro.