This cat is … slightly camouflaged. Photo (CC) Tambako The Jaguar (but yes, this is a snow leopard).

Mac OS X 10.6.3 looks like it may be a significant update for graphics performance, but good luck trying to figure out what’s changed from the vague update log. There is mention of “compatibility issues with OpenGL-based applications.”

Our inside sources tell us that previous seeds did mention specifically Quartz Composer fixes related to performance, an issue about which some QC devs had complained.

10.6, for its part, included major updates to Quartz Composer, with some really spectacular work ranging from OSC support to OpenCL, workflow improvements, and performance gains. Those changes are fairly well-documented in a document on the Mac Dev Center:
Quartz Composer Release Notes for Mac OS X v10.6

But with that came a few performance glitches – not the good kind. It appears 10.6.3 may resolve those issues; we’ll know following additional testing.

The update also promises improved “reliability and compatibility of QuickTime X.”

More evidence that Mac-based visualists should update to 10.6.3 comes from Macworld. Rob Griffiths is able to uncover updates to ATI video cards, and VMware – of all people – say that 3D performance is improved in the update.

Inside Apple’s OS X 10.6.3 update:
What Apple’s release notes don’t tell you about the latest Snow Leopard update

It is a little embarrassing when a staffer for Macworld has to guess what’s in an OS update. I would love to see more detailed update documentation from Apple. I think it really is best for everyone when those who want more detailed answers can get them. In fairness, when I have asked Apple for support in finding out details, the folks I’ve worked with in PR have been really helpful. But Apple does great work on their OS, by and large – so why not talk about it in more detail?’

While the 3D info is hard to find, there are lots of performance and reliability fixes, as well as some security changes. Official Apple-documented changes here:
About the Mac OS X v10.6.3 Update [Apple Support KB]

Of course, real-world testing is what matters most to us – regardless of how well changelogs are written. So let us know how 10.6.3 works for you in the field, or insight you have on any OS.