Hi Dave,
Yes, I agree that often the 12 mm setting is too wide for a natural look but taking out a wall so I can back up is not a suitable alternative. (ha ha)
What I mean to say is that many pro shooters have to make a living shooting interiors where the space is too limited for a natural look.
I am however a proponent of exaggerated perspective to make the mundane look spectacular. Architectural Digest is still a bit of an institution when it comes to wide perspective shots often done on a Hassebladt Super Wide. I also get very nice images where others get a typical amateur result due to the limitation in their own mind to let the viewer be the judge of what looks good or not, wide or too tight! Ok, do not place certain objects at the edge if they are going to dominate the shot but that is just common sense to me.
The other issue is that 12 mm on the D300 or any other cropped format is actually a longer lens when it comes to the perspective, the 12mm is like using an 18 mm lens on a full frame camera. Using the widest setting of 12 mm which now effectively is 18 mm and then also shooting down from a high point to get the results of a shift requires even further cropping after correcting for keystoning. Likely the end result is a 24 mm effectively or even less. At f:10.0 the lens is at its sharpest and the depth of field is enormous.
The 12-24 mm is not a substitute for a shift but it is a workable alternative if you are a Nikon shooter. As this 12-24 is a Sigma full frame lens, I now also have the opportunity to use it on a full frame film body or one of the newer D3 or D700 cameras. You see that I do not use the Nikon wide lenses as at the time I purchased this lens there was no other lens like it. I use this lens a lot and strangely when I convert with Nikon Capture2 the visible chromatic aberation is removed automatically. I do not know why this lens exists in the NC2 software but it does. The slight barrel is easy to remove and the lens is remarkably sharp. You must realize that absolute sharpness is only a secondary trait of good photography. Until today I still feel that the right angle and the right lighting are more important than the highest measurable sharpness. Sharpness of a lens is more a function of contrast and pleasing transfer edges. The only drawback of this lens is the flower petal lens hood that is built in. With a polarizer I need to zoom in or I get heavy vignetting but many times I only have unimportant and empty corners which I simply clone in if I have to.
Bottom line, I get the shot while many others do not!
Rinus

Well i just found this and just enlisted ? i make photos of Chalet
and hotels in switzerland nikon D3 and D700 and love my 17 35
zoom, keep thinking about the 24 tilt-shift but not sure if its wide
enough rooms are small here even at the top end of the market
and on the internet as a 5 by 7 max and most of the time smaller .
will i see the difference in using the 24 TS or the 17 35 .I guess
i will have to try my new 24 70 on the D700 and shot at 24 to
to see if i can do it i used the 24 70 for my details most of the time
Joe www.rockzermatt.com