I feel like I have to clarify a few things as someone who has been
playing with ia64 hardware for the last year.  I'm not sure not sure if
I'm free from the NDA since the chip is released, but what the heck. :)

As far as Linux is concerned, you can run any Linux Intel binary on
Itanium.  The chip does a switch of some kind and runs the code
natively.  It's not fast, but what do you expect when it takes four
years for Intel to paste on 32-bit support to HP's 64-bit processor?
Sure you'll want to recompile apps for speed, but the Linux distros ship
with i386 libraries for compatibility.

I don't know what's going on with Windows on 64-bit.  I know that work
is being done there, but I don't know how much.  

Also, in response to Brian's comment on ia64 as a supercomputer chip,
HAHAHAHAHAHAHAHAHAHAHAHAHA!   You must be kidding.  Sure, it's mostly a
server chip at this point, but you're not going to see any Itanium
supercomputers.  Sure, you'll see some clusters and some 16p servers,
but not supercomputers.

Nate