According to the Ultimate Metal Forum, the highest number of notes per second is 18, played by Shawn Lane, a musician who died in 1963 - you can see the full list here. A number of other guitarists have also come close to this, reaching anything from 12 to 17 notes. However, this list isn't official.
If you put 'most notes played per second on guitar' you will get a lot of wild claims, but nobody seems to have tested them properly. Certainly, it's hard to see how anyone could play much more than 18 notes per second, if that, and Shawn Lane is generally accepted as the fastest guitarist of all time. You can hear him on Youtube to get an idea for yourself if you click here.
Recently it has been claimed that Randall Patilla is even faster at 23.5 notes, but not sure how you would confirm this.