Safari 4.0 Beta
Safari 50%
Window Server 12%
OmniWeb 5.9
OmniWeb 36%
Window Server 5%
Camino 1.6
Camino 33%
Window Server 5%
Here are some screen grabs showing each browser's performance. Further remarkable is the fact that Camino split the workload across the cores nearly evenly. I tested on a Macbook 1.83GHz Core 2 Duo with 2GB of RAM running OS X 10.4.11.
[robg adds: I did a quick test using my 2.66GHz Quad Core Mac Pro (running 10.5.6) and an HD-quality video on YouTube. I also added Firefox to the mix, and my results were a bit different than above. On my machine, for the video I was testing with, Camino was also the clear winner at around 80% CPU usage. However, there wasn't any notable difference between OmniWeb, Firefox, and Safari 4.0 Beta -- all three were in the 115%-125% range. More experimentation is needed, but it definitely seems that Camino does the best job of minimizing CPU usage during Flash playback.]

