As much as I enjoy all these road courses, none of them will ever host an F1 grand prix. The biggest reason is that neither the tracks nor the areas can accomodate the amount of people and stuff required to make money (or lose as little money as possible). I don't think any of the road courses are safe enough either. In the issue of Road & Track after the news broke that the 08 USGP was cancelled, they talked to the people who run the Long Beach Champ Car race and they said 'no way.' In another R&T article called "The Anatomy of a Racetrack," the designers of Miller Motorsports Park in Tooele, Utah, said their track was the only one in the country besides Indy that had F1-spec facilities. However, they were doubtful that F1 would every come there. So, personally, I can only see the USGP coming back to Indy (and I think it will happen).
I left out discussion about races running through streets because I really have no idea about all that. But if the people at Long Beach said it would never happen there, it would take something special to bring the USGP to a downtown street circuit. Again, after the news broke about the 08 USGP, Frank Williams was asked where else the USGP could be held and he said "a certain gambling resort," so I guess Vegas is the leading street-circuit candidate. But like I said, I personally think it will be back at Indy by 2010. Cheers everyone, enjoy the Malaysian GP!!