Optimized? Hey its jusy amazing that enough information has reached open developers to do this at all.
Yes, optimised, as it stands the 3d portion is a little on the slow side.
As for amazing? A year ago the OSS driver was little more than a Vesa frame buffer with those words crossed out and replaced with "ATI display driver" put in in crayon. Since then, the full gamete of 2d capabilities has been added and yes whilst slow, usable 3d (more than fast enough to run compiz type effects, or basic games for instance) has come into being. It is a testament to their dedication that they've come this far, this fast.
For some reason ATI has always wanted to keep the exact way their products operate a deep dark secret (and Nvidai hasn't been much better). Then they've tried to force us into lame proprietary drivers.
In of itself I have no truck with this, as nVidia shows, it can be done well. However the proprietary drivers for ATI/AMD graphics products has always been a hateful, spiteful experience. One which, if you're exceedingly lucky, you might get working, but more often than not will leave you frustrated and cursing the Canuks who created them.
To have something that works out of the box, won't break every time you update the kernel is a wonderful thing

It would be nice to have a competitive third company in the market that was serious about open drivers.
Intel for starters, I believe that VIA's graphics drivers are with a few exceptions quite open too.