The newer GCC compiler (the 4.4 series) in the Fedora, RHEL, and Ubuntu updates are likely the reasons for the GraphicsMagick speed-ups. GraphicsMagick utilizes OpenMP for its multi-threading, which is better optimized in newer GCC releases.
For those into computational biology, HMMer is running faster with all of the new distributions. Red Hat Enterprise Linux 6.0 Beta is on par with Ubuntu 10.04 LTS.
MAFFT is also running better.