Tilt and shift both have their uses, of course tilt at 90 degrees becomes swing.
I currently have two tilt/shift lenses (24L2 and 90) but unfortunately even I am surpassed by the mighty (figuratively speaking) Canon Bob who has three 24L, 45 & 90.
They are some of the most useful lenses you could use and on my 1D Mk3 i would have kept the 24L2 as my standard lens, now I have 1Ds3 I suspect that the 45TSE would make a better standard lens.
There is another fantastic use for a TS lens you can expand the sensor size and resolution to MF standards, if you shoot in portrait mode on a 1Ds3 and take a 12 degree shifted image to the left and right, and stitch them together you will end up with an image 7226 x 5627 pixels and a 116MB file.
This is a full size representation of a three image stitch that I have just taken on the 90mm TS-E in portrait mode with 11, 0, 11 degrees of shift and resized for the web. This gives an angle of view along the horizontal similar to that of a 60mm lens.
This is a 100% crop from the original high res image!
Another 100% crop