The new Perspective crop tool in Photoshop CS6 Beta is great. I find it very useful for correcting the perspective when I take pictures of my paintings. I try to shoot them the straightest I can, but there is always some distortion so with previous versions I had to crop the image to the rectangle that confined the painting and then select all, transform and pull the corners with CTRL to match the corners of the painting to the corners of the image. Even then, I was not sure the image had the correct aspect ratio since it was made by hand.
Perspective crop makes all this in just one step and calculates the correct aspect ratio but I think It can be enhanced a little more.
Just look at this picture:
I took it in the Subway. The problem here is the poster is attached to a curved surface. Perspective crop is helpful here:
But there is still some distortion after the cropping. I tried all distortion filters and lens correction, but no help since they are oriented to straighten curved walls due to lens distortion, not really curved walls. The only helpful tool was Warp Transform:
It gets the job done, but again, you have to figure out the aspect ratio by eye and the result is not geometrically perfect. Also, due to the curved wall, the image is compressed at the top and bottom where the wall curves to the camera but not at the middle where the wall is more straight.
But, ¿Wouldn't it be great if in the Perspective Crop you could just pull the side handlers (marked as 1 and 2 in the following mock up) of the mesh with CTRL pressed to do something like this?:
Just think of the possibilities! One of the uses of the perspective crop you mention in the previews in Youtube is to obtain textures for a 3D object. Well, this is good when the texture is from a flat surface but what about cylindrical or spherical surfaces? you could photograph them and extract textures ready to apply to cylindrical or spherical 3D objects!
Just in case you hadn't realised , the perspective crop tool is available in CS5. It's just not so obvious.
In CS5 draw out a crop box - and then look at the options bar. You'll see a checkbox labeled 'persective crop'. Tick it and you'll be able to pull the corners independently.
I like your idea for the extraction on curved surfaces. I've had to do the same work myself in the past - perspective cropping images for 3D textures.
I think with the new technologies for adaptive wide angle, lens correction etc, your idea might well be possible.