Full 64-bit functionality indeed hinges not only on applications being 64-bit capable, but also the hardware and the OS. Apple's hardware has had certain 64-bit functionality for some time, but 10.4 and 10.5 haven't gone the distance in this regard, making it difficult (or impossible) for developers to write true 64-bit apps.
A couple of years ago, Apple decided that it would no longer support Carbon Frameworks which have been used on PPCs. This threw many developers for a loop as many developers had already worked on 64-bit Carbon Frameworks to no avail. These frameworks had to be rewritten with Cocoa Frameworks in mind in order to support 10.6.
What that means for developers is that all software has hit somewhat of a brick wall-- 64-bit processing within a 32-bit OS kernel. It's getting there, but Tiger and Leopard have been gradual steps to getting there.
Once Snow Leopard is released, we will see the transition accelerate. There WILL be some additional wait (however long or short) for DAWs to go all-Carbon and 64-bit capable. Then there are all of your favorite plugins and fx in addition to your favorite virtual instruments which will have to make the transition. Not all developers will be able to release their updates at the same time, but let's hope that the most important software we need will be released within a reasonable amount of time. It won't make sense to have Snow Leopard if half of your software (or PPC hardware) is not compatible. This is why, imho, OSX 10.6 will be a lot less expensive than other OSX updates/upgrades. Users will likely be hit with numerous upgrade fees, and this can be costly. Hopefully, some developers will be merciful by offering free updates or at least taking Apple's lead and keeping the prices low. Otherwise, there could be a lot of frustrated (and bankrupt) Apple users out there.
We may hear further news from developers during the summer trade shows, but I have a feeling that we will hear a lot more by Winter NAMM, 2010 (USA) and certainly by Musikmesse (EU) in March, 2010.
I probably won't "buy any green bananas"
until 10.6.1 is released just to give developers and Apple a chance to iron out the initial wrinkles. Otherwise, I could be out of business if there are too many things which just don't work.
This article might help explain things a bit better (although some of the information about release dates was based on confirmed information from late 2008)
From:
http://www.appleinsider.com/articles/08/10/28/road_to_mac_os_x_snow_leopard_64_bit_to_the_kernel.html
When released to developers around spring and to end users a few months later, Snow Leopard will support using a 64-bit kernel on all Intel Macs with 64-bit CPU, such as the Core 2 Duo.
A 64-bit kernel requires all of its extensions to also be 64-bit. Kernel extensions or KEXTs include drivers for audio hardware, graphics adapters, networking, certain printing components, and other devices on the logic board or attached as peripherals. Until Apple delivers 64-bit versions of the nearly 300 extensions it ships with Mac OS X (not all of which will need to be supported on 64-bit Macs; many are legacy), it is limiting official 64-bit kernel support to a subset of Macs in prerelease builds of the new operating system.
The 32-bit kernel of Mac OS X
Snow Leopard will deliver the first 64-bit kernel for Mac OS X. Earlier versions of the operating system, including today's Leopard, can run 64-bit software but do so using a 32-bit kernel. More accurately, whether running on 32 and 64-bit CPUs, Mac OS X loads the same kernel image and run it as a 32-bit process, although when run on 64-bit hardware, the 32-bit kernel switches into "long mode compatibility mode."
Apple's current implementation allows the existing 32-bit kernel to run both 32-bit and 64-bit applications at once, as well as being able to handle 64-bit virtual memory allocations, giving 64-bit applications and background tasks the capacity to allocate memory spaces larger than 4GB when working with large data sets. In Tiger, 32-bit graphical apps could create a 64-bit process; under Leopard, Mac OS X can run full 64-bit graphical apps.
Leopard's 32-bit kernel has been fitted with enhancements that handle copying between 32 and 64-bit user address spaces, and its syscall and trap handlers are also 64-bit code. This hybrid design enabled Apple to deliver a kernel that could run 64-bit apps without needing to immediately deliver 64-bit kernel drivers for it, nor to require third parties to all ship 64-bit versions of their drivers.
As described in earlier coverage of Snow Leopard's 64-bit features, Mac OS X can also currently use various techniques to use more than 4GB of installed RAM, the limit imposed by 32-bit memory addressing, despite using a 32-bit kernel. Intel's hardware uses a method called PAE to enable certain Mac models to address as much as 32GB of installed RAM, despite Mac OS X's use of a 32-bit kernel.