DRM has been removed from the Witcher 2 in the latest 1.1 patch due to users experiencing problems with the retail versions. As a result of the DRM removal, game performance has increased by 5-30%.

Here are the official v1.1 patch notes from the readme:

• The process of installing and activating the game is now easier and more stable. SECUROM copy protection has been removed entirely, making the game DRM free!
• The hardware configuration auto-detect function has been corrected, resulting in improved game efficiency.
• Game efficiency has been improved. Game now runs 5-30% more efficiently and game loading has been accelerated. Efficiency increases will vary depending on system configuration and game version. Owners of boxed versions of The Witcher 2 are likely to notice the greatest improvements.
• Bugs causing the game to crash, especially while saving game progress or loading saved games, have been corrected.

Downloading the latest patch:

If you purchased the game on Steam, it will auto-update the game to the latest patch for you.

Note: If you purchased the game elsewhere, there may be a different patch method. Check the site which you bought the game from for official instructions. (Direct2Drive / GoG.com)