The Witcher 3: Wild Hunt on PC will receive a new patch on Monday (June 1) which will carry fix for the nasty "no XP Glitch" in the game. In addition to this, CD Projekt Red clarified that this No XP Glitch in The Witcher 3 won't have any impact whatsoever on the game balance

Marcin Momot, CD Projekt Red Community Manager stated:

We would like to let everyone know that we are aware of the XP glitch players are reporting and we are working to have it fixed as soon as possible across all platforms (Monday for PC & patch 1.04 on consoles in the following days). 

At the same time we want to shed some light on the issue. First of all, it doesn't impact the game balance in any significant way. Also, you will be able to finish the game with your character achieving a level within the threshold we had in mind when we designed the game. 

We hope this clears things up a bit. Again, rest assured, we won’t stop working on improving the game and there are more patches coming in the near future.

In related news, good news Nvidia users.

A few days ago Nvidia reported on working on driver updates to address Kepler issues with The Witcher 3. It appears though, that Kepler owners will enjoy a performance boost in several games with the new driver. Nvidia's ManuelG noted that the upcoming drivers will offer a universal fix for Kepler GPUs that will boost performance in various PC games. That's good news indeed, especially considering recent allegations that Nvidia is crippling older GPUs performance in the latest games in order to promote its new Maxwell series, something that is quite evident in The Witcher 3: Wild Hunt, as the game runs considerably worse on Kepler GPUs compared to Maxwell 900 series.