This shit comes out in like 5 hours! WHO'S READY FOR PORTAL 2?!?!!
Also in before "wheres the sdk??" (will it even be released with the game?)
Also in before "wheres the sdk??" (will it even be released with the game?)
That said, I expect custom maps to be made within days of release. And they had better be uploaded to TWP! 
But I have a feeling VALVe will have the SDK ready a little earlier than a month. I remember them saying something about having it ready at release, and while I'm not that naive, I think they'll be pretty good about it. Especially with all the hype they're throwing up.