The lights are on
That's strange, because before even this announcement for the game was made, I had a dream where I was playing Portal against guards that had guns. I would defeat them the same way you would with the turrets, either having them fall or dropping an object on them.
The only major difference they had from the turrets in my dream was the fact that they could chase after you when sighted.
Also in my dream were gravity-like shoes that would auto-place you on the closest surface, sort of like Super Mario Galaxy. I'm not sure that would actually do well in Portal.
Lastly, my dream included combat with other enemies with portal guns, which was about where my dream ended.
Pretty in-depth dream though, huh?