*Update*
You now rotate from your new position when comeing out of a portal
One thing i noticed, if you spawn a portal on a wall, and the other portal higher up on the same wall, you come out of the portal facing the way you came in, which results in you getting stuck going between portals, if you hold down the button in the way you were going.
I have resolved this now, you can't run unless you are facing the right way up.
Add terminal velocity. Funky stuff happens if you make the portals just fall into each other. I seriously thought the game was going to explode... That and then I shot a portal and I glitched into a wall(this is after falling for a while).
I removed terminal velocity to demonstrate how the portals can work at extremely high (actually unlimited) velocity. The 'Funky stuff' would be the view shaking uncontrolably and your speakers making an incredibly irritating buzz? As for the getting stuck I have just been fixing that (hopefully)

Also I have just fixed another glitch where you could rapidly click while hovering in a portal and get paused for a moment, then slowly start getting propelled faster and faster and faster...
Download link is in the first post