This 15 minute video is a demo of the Portal Speed Run. Before you yell “For science, you monster!” yes, the player does make use of glitches. In fact, you can find a list of glitches deployed here. There a lot.
Be prepared to spend a lot of time watching elevator doors. They’re clearly the slow common factor in the game.
The record is just over 9 minutes and 25 seconds. Think you have any chance of challenging it? Bring on Portal 2!