Ref:"Intel's EM64T. Is this a "serious" competitor to AMD64?"
Yes and no. Since Intels only 64bit enabled chip is based on P4 architecture, the Prescott...and that core has run into a thermal brick wall it behooves Intel to stall 64 bit Windows until they can add it to the Pentium M core which is the future for them. Intel walks a fine, tenuous line but they still control a lot of standards.
People I know that beta test Windows XP 64 tell me it still crashes too much.
aleph0, on EM64T as an Opteron competitor, the first implementation is a rush job meant as a stop-gap measure to show that Intel will respond to the competition. Look to future versions to be more competitive. However, Intel definitely is earning a 'follower' reputation with new x86 processor technology!