In contrast to my other article on QuickTime H.264 encoding on Intel Macs, it seems that QT H.264 decoding is actually very fast on Intel Macs. This post by Xool shows that a Core Duo 1.83 with Radeon X1600 can play back 1080p and 720p H.264 video at the full 24 fps with only 40% and 12.5% CPU usage respectively. That's even less CPU usage than a Dual G5 2.0 Power Mac. Given these results, it seems likely that Apple has incorporated GPU-assisted H.264 acceleration into its Intel Macs sporting the ATI Radeon X1600 series CPUs.
Furthermore, Xool's post suggests that QT H.264 encoding speeds are pretty good too on the Intel Macs. The 1.83 GHz Core Duo iMac was about a quarter slower than the Dual G5 2.0 Power Mac, but significantly faster than a G4 1.67 PowerBook. These results however are tempered by the Ars iMac Core Duo benchmarks which show that the Intel Mac is barely faster than a G5 1.8 GHz iMac at QuickTime video encoding. Unfortunately, it doesn't seem H.264 was specifically tested in the Ars video encoding benchmarks.
With this GPU-accelerated H.264 playback and the announcement of slim-line slot-load Blu-ray drives, it looks like the MacBook Pro and the iMac lines may be primed for the Blu-ray push later this year.
Craig Wood has now reposted the benchmarks as a formal review.