J'ai effectivement trouvé ceci (source ici):
I have finally fixed my slow performance issues with LR2! Today I did a bit of playing around with different performance settings. I'm using LR2 on a HP Pavillion 6258se Laptop. It has an 80GB Hard Drive, 2GB of Ram and the processor is a 1.8 GHz AMD Turion ™ 64 X2 Dual-Core. I had Windows Vista installed months ago but I downgraded back to XP due to Vista issues. First I opened the windows task manager so I could monitor the performance of Windows while using LR2. I noticed when using the develop tasks the performance stayed around 50%. When I used the retouch brush tools the performance still stayed around 50% but the brush tools were still slow. The more I brushed on the image the slower the brush refresh became. This told me that there must be a video performance issue and not necessarily a processor problem.

Here's how I fixed the problem.

1. I right clicked on the desktop and clicked NVidia Display/Laptop
Dispay.

2. Clicked on the Performance and Quality Settings

3. Under Active profile Click Global Driver Settings.

4. Under Global driver Setting click in the dropdown view advanced settings.

Changed the following settings:

Images setting = High Performance
Force mipmaps = None
Trilinear Optimization = Off
Anisotropic mip filter optimization = Off
Anisotropic sample optimization = Off
Triple Buffer = Off

Without even restarting LR2, the brush tools worked with no lag or delay no matter how much I brushed on the image! They were just as fast as using the sliders in the develop module!

I hope this works other Nvidia users having similar issues!!

Mark
et une autre info sur les forums d'Adobe ici qui indique qu'une piste serai désactiver le "nView Desktop Manger" :
I use the "nView Desktop Manager". It was fine for Lightroom 1.4 but causes real performance problems with Lightroom 2.0, in particular when loading the Develop Module.

Select the Develop Module then close Lightroom. The time taken between starting Lightroom and for it to become responsive with nView enabled was around 25 seconds, with nView disabled it takes around 7 seconds.

I had similar performance issues whenever I used the Spot Removal Tool or Adjustment Brush, and in particular the first time loading the Development Module within a session. Basically the tools in the Develop Module are now responsive whereas before it took 3 to 5 seconds each time I clicked on one of them.

To disable "nView Desktop Manger" for Lightroom only;

Right click the desktop > nView Properties
OR Control Panel > NVIDIA nView Desktop Manger

then;

Applications > Add... > Browse... > C:\Program Files\Adobe\Adobe Photoshop Lightroom 2\Lightroom.exe > OK > lightroom (Application) > Disable... > CLEAR Enable nView Desktop Manager for this application and/or class > OK > OK
Bon, moi j'ai aussi une nvidia mais je n'ai pas encore remarque de lenteur particulière ; je ferai quelques tests prochainement. Si toutefois vous avez des retours sur ces conseils, je suis sûr que beaucoup seront contents de les connaître :-)