32-bit or 64-bit

[pkaplan1]

I just got a new Thinkpad T400/4Gb w/ Intel video at work and am trying to 
decide which version of kubuntu to install, 32-bit or 64-bit.

What are people's experiences with Flash and VirtualBox on 64-bit?  Are they 
reliable?  (Does flash install in 64-bit with the restricted extras package?)

Is there really a noticeable performance gain w/ 64-bit?

Wireless?

Power management?

X, especially w/ multiple monitors?

Any gotchas to look out for on 64-bit?

TIA
Paul