The No Intro Videos Mod skips all intro videos except the logo by CDProjekt.
Market Price Mod makes buying and selling prices within markets more fair to the player. It reduces the 24:1 ratio between buy to sell prices and reduces it to 5:1 as seen in the original game.
For people having problems with the size of text on large resolutions or on small displays, getting any variation of the Comfy Font, and placing the .dzip in the CookedPC folder will make it bigger and more visible.
Full Combat Rebalance is a mod created by the developers of the game. It includes many changes, including an 80% increase in responsiveness per Geralt's animations and decreased time for returning to exploration after combat. The file is 1.5 GB in a compressed format.
AI Upscale Textures contains over 600 character and object, 1100 original environmental and 150 weapon textures with increased resolution quality x2 (ie. 512x512>1024x1024, up to 4096x4096) in AI Upscaled Characters Textures X2 VERSION OPTIMIZED, AI Upscaled Enviromental Textures X2 VERSION OPTIMIZED and AI Upscaled Weapons Textures X2 VERSION OPTIMIZED. With minimal impact on performance.
The Anisotropic Filter can be activated from the control panel of AMD (Catalyst Control Center) or from the control panel of NVIDIA (NVIDIA Inspector) but the impact on the performance when placing AFx16 is evident in medium/low computers. The difference between the disabled AF, x4 and x16 is shown in the next three images. The difference between 4 and 16 samples is minimal, but you can see how the detail is clarified in the rock and in the grass near Geralt:
The Witcher 2 makes use of a sharpening filter that increases the sharpness of the game's visuals. While this setting has a negligible performance impact it does cause increased aliasing and adds an unnatural sheen to many objects, if those bother you it can be disabled with an INI tweak.
Users that are using 16:9 resolutions are able to use HBAO+ in the game via Nvidia Inspector. 
The Ubersampling option completely prevents HBAO+ from working, but it does work with DSR. 
The Witcher 2
Ambient Occlusion compatibility
Ambient Occlusion setting
Ambient Occlusion usage
Enabling the following options will result in a significant reduction in in-game frame rate:
Note all other graphics options can be enabled/disabled with little or no FPS impact. Note that whilst 'Texture Downscaling' has a significant visual impact on the 'High' setting, reducing downscaling to 'Low' or disabling it entirely can drastically improve the look of the game with very little performance impact.
and save it
There are two possible causes for this issue:
The game attempts to reinstall the Microsoft .NET Framework 4.0 every time the game is launched.
Open Notepad, and enter this code:
;For 64 bit systems (x64)
Windows Registry Editor Version 5.00
;For 32 bit systems (x86)
Windows Registry Editor Version 5.00
Save as a .reg file, and then double click on it.
Patch 2.1 is meant to fix communication between the game and the Witcher forums arena leader boards. Since the update, many people have experienced an error that says The application failed to initialize properly (0xc0000142). There are a few ways to fix this.
A special cut-scene should be played off, but instead you receive a black screen and only hear Dandelion's voice.
If you have AMD Gaming Evolved installed, make sure the program is not running while playing.
Large number of saves will result in longer loading times when you open the menu for loading a save. To fix delete unused saves or move them to a backup location.
When using ambient occlusion forced through Nvidia Inspector, there is a noticeable flicker while moving around, this is caused by higher-detail meshes being loaded in. To fix this issue, in the user.ini under the "rendering" section, increase "MeshDistanceScale" to a much higher value; e.g.: "MeshDistanceScale=100". This will also reduce non-AO related pop-in and in general make distant objects look better. Note that this potentially has a performance impact, test different values to see what works best on your system.
The Linux port is not native, and is packaged in a Wine-like compatibility layer called eON. eON is used for some other titles (such as Stronghold 3). It is not based on Wine, but has a similar reimplementation of the relevant Windows APIs.