The SP1 64bit update found its way onto some systems after being released in Windows Update. It was meant for TechNet subscribers only, and has now been withdrawn.
The wait for public release goes on and is scheduled for sometime in March or maybe even April as demand will be high high high, and will make it onto your system as long as there is no conflicting driver issue.
I noticed that there were two 'optional' nVidia drivers (not the video kind) on WU recently which may be part of the driver incompatibility fix. I did install them and without issue.