I recently upgraded to the palit gtx 260 sonic. I thought i'd share my experiance as there has been no linux reviews. First off this cards only downside in many windows based reviews is the card runs at full clock speed all the times (bios issue) and I can confirm this happens in windows, but strangely the thermal management works fine with linux drivers. There are 3 speeds steps visable in nv settings and you can see it changing.

My system q6600 @ 3.2ghz 6gb ddr 800. Ubuntu 9.04 64bit

The card has allowed me to run nexiuz 2.5 on the highest settings, I even adjusted some of the extra settings to insane and it coped at 1920 x 1200.

benchmarks...

unigine tropics 48fps 1920x1200

kde 4.3 performance.

I cant really see any performance increase over the 8800 gt @ 1920 x 1200
frames appear to drop while resizing but not to an unusable level.

Drivers stable no issues found here. I installed the latest drivers from the nvidia site.