Performance decrease? Everything will ship 64-bit? What? Why? This doesn't make any sense at all.
Let's do an example. I have a program that does a whole bunch of 16-bit math (16-bit photoshop filters for example). So if all of my math is 16-bit, how does running on a 64-bit OS help or hurt the program?
If Apple ships all applications as 64-bit applications, what happens to all the users with 32-bit machines? I'll give you a hint: 1) They won't be able to run the application. 2) Apple will sell both a 64-bit and a 32-bit version (both Universal of course)...so we'd have 4 different executables in 2 different packages...and all 4 have to be tweaked and debugged and tested.
The vast majority of applications don't need 64-bits, and in fact won't even be able to take advantage of it. How will a 64-bit version iWeb be better than a 32-bit version?
Just look at the Windows side for a moment...very few use 64-bit versions of Windows....and of those who do, very few have 64-bit versions of the software that run on it. Most of the video and modeling, etc is done on 32-bit versions of Windows and appropriate software.
All I'm saying is, don't get swept up in the hype...they know they can sell numbers...people who have no idea about computers can see that 64 is bigger than 32...SO IT MUST BE BETTER. In reality, it will be many years before you have to have a 64-bit processor. Look how long the transition from 16-bit to 32-bit took. We're probably only half way through the transition... The SPARC went 64-bit in 1994, the Itanium was 64-bit in 2001 and the Athlon 64 came out in 2003. The first two are hardcore workstation/server chips, and it has only been recently that 64-bit in that space has become a "must have" feature. It'll be a while...it's all marketing-hype at this point on the PC (as in Personal Computer, not Windows Computer). If you want to wait for the 64-bit chips, then great...but it's not all everyone is saying it is...at least not now, or in the next few years.
Here's one more question. If Apple upgrades the MBP tomorrow and the only change is to go from the 2.16GHz Yonah, to the 2.16GHz Merom, and they increase the price by $100, will you be mad?