Same with me, just downloaded the GenuineCheck program, and am now downloading the service pack with the key it gave me, so I'm assuming mine was found genuine (it didn't explicitly say it was genuine).
Usually there's always a benefit with installing a new SP however this one doesn't have many changes that the end-user will notice. Most of the changes are for Windows Server 2008 which includes RemoteFX support (offering a better remote desktop experience). I'm in no rush to get it myself even with a legit copy of W7
I installed it tonight, and not long after I used System Restore to reverse it because my computer was soo incredibly slow that the mouse would lag and low resolution videos would play at like 1frame/2seconds, don't know if it was the service pack or the flash update I did right after, but as FrozenIpaq said there isn't much benefit from it, so I just uninstalled it, it's back to normal now.