wbmw, some comments -
I think it will be very difficult for AMD to get some developers to port to 64-bits when the architectural differences don't make much of a difference for their application.
That is a 'so what' item. No one waits until all the applications are ported for their buying decision. For that user it is sufficient for one compelling application to be ported, and that everything else still works. For AMD, it is sufficient that enough compelling applications are ported so that most users can see the benefit in at least one of their apps.
The situation may be worse if the 32-bit version degrades even worse under a 64-bit OS because of the WoW switching.
This is a more complex item and needs some focus. First you have to differentiate between the launching of an app, and running it. When it is launched, WOW64 has to set up a compatibility mode environment for the 32-bit app. After that the app makes system calls to the Windows stub just like before. That stub then has to make a gate-style call to the real underlying function. The cost is a few instructions followed by a processor context switch to 64-bit mode, which has overhead similar to a traditional 32-bit call gate.
Once the call is in 64-bit mode in the OS then the application gets the benefits of 64-bit optimizations (simpler memory model, miscillaneous OS optimizations). When the call returns then the stub has to do whatever is needed to present the results correctly to the app, a few more instructions.
So the application pays a small penalty in making the call & returning, and then gets a small benefit within the OS. What is not known is whether the app gets a net benefit or net penalty.
Microsoft is not going to offer Windows 64 as their primary OEM distribution. There are simply too many drivers to port, and 64-bits requires *all* of them to be ported. Microsoft is only offering it as a niche product for those interested in the increased memory capacity, and they'll probably charge a premium for it, too.
You have not presented any support for this view, and it runs contrary to earlier MS releases. It is more consistent for them to make one distribution for XP Professional which contains both versions at the same price. (Remember how many architecture versions were on the old NT CDs?)
My prediction is that Windows 64 will be underwhelming when it launches.
Hard to argue with that! It is the Microsoft way, after all. :)
Expect that it will have all the drivers needed to support the hardware that will be offered by the manufacturer for that machine. Expect that there will be a few impressive, highly optimized apps that will be benchmarked and a whole slew of quickly ported apps which won't benefit from 64-bit.
The press will love it, just like they love everything from Microsoft. There will be glowing articles talking about how the new 64-bit universe is here.
Side note: This discussion hasn't addressed a whole class of 32-bit apps that will benefit, even on the K8 AthlonXP. That is, applications that benefit from more than 2GB of DRAM. The PAE implementation in Legacy Mode enables a 32-bit OS to address the full address range (52-bits, I recall) and to provide a full 4GB to multiple applications simultaneously. As discussed here in detail, the SP2 version of Windows coming up will support this mode, required for the NX bit.
So, you want to have an 8GB PC running existing 32-bit Photoshop and Illustrator with 4GB allocated to each app? No problem!
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