I played around with the editor a little last night, and from the first look I have to say holy crap indeed. The editor seems like it's all it's cracked up to be. Even without reading any instructions I could easily place buttons and connect them up. The real challenge, as I mentioned before is coming up with good test chambers.
Have you ever played Portal Prelude? It's a fan mod for the original game, a it is a prequel (although I disagree with its portrayal of GLaDOS, but that's neither here nor there). It's technically a very well made mod, and it is fun and challenging, but too often the challenge relies on fancy jumping and not clever use of portals. For example placing two portals vertically and falling endlessly and then (while falling) placing a portal to fling yourself to the correct place (very hit and miss). Or worse, placing a portal on the ground and one on a wall to fall through a endlessly to build up speed. I'm not saying it's a bad mod (it's not), but they seemed to me to have missed the spirit of the game: difficulty through fancy portalling, not fancy jumping.
I also agree on your deep editing features. The editor could have two levels; basic, like it is now (I'd add being able to skin it with the various Aperture time periods), and deep, where you can manipulate every aspect.
Anyway, if you build and test chambers drop me a line, I'd love to give them a try.