No - they run at the old 320 x 480 resolution
It may have, but iPhone apps don't run at that resolution on the iPad: they run at 320 x 480. Please check your facts before making sarcastic comments
Just in case you still don't believe me, here are three screenshots of Spotify (an iPhone optimised application with Retina Display support)
The first is on the iPad at "normal" size, the second at 2x size. The black border is the rest of the iPad screen. The last one is from my iPhone 4
As I said before, iPhone apps look terrible on the iPad...
(I believe there is a solution for jailbroken iPads to use the full resolution but there is no jailbreak for iOS 4.3 yet)