Image stablization makes a huge difference at any focal length, I just start failing to see the purpose when you get these slow 18-55s.. I mean its nice to have, there are times I wish I had a 18-55 VR isntead of my non VR just because I was taking night shots at 1600 iso hand held.
Stablization it really doesn't matter how fast you're taking the picture once you get over the 1/800 range, 1/500 and you start seeing plenty of motion, VR/OS/IS doesn't stop this motion, it floats the lens so everything else flat like it should be.
Here, put yourself in this situation, lets say you're taking a photograph with the lens I want, the 70-200 2.8 VR, it is a close up shot of an airplane prop (sorry was at an air show this morning), on a cloudy day, and you want to shoot at 2.8 so you put an ND filter or two on it to slow the speeds down so you get the depth of field to keep the 2.8, so here it is.. normally you would be taking a 1/800 which you can see probably 10 degrees of prop motion typically, but here you are with 2 ND8 filters on this beast and are shooting at 1/100 (not that anyone would do this, at 1/100 you would have no prop at all it would all be a blur), but anyways because you're shooting at 1/100 at 200mm, you would have to know some good breathing excercieses to pull this off without blurring the entire photo, so VR comes on and floats the lens elements and keeps it all steady so you're still shooting at a very slow speed, but everything is still sharp.
With my 55-200 4-5.6 VR, I have taken shots well below 1/50 at 200mm at 5.6 and VR has saved my life plenty of times, image stablization makes a huuuuuuuuuuge difference, it is honestly worth the expensive price you save so many more photos.
Someone else may say, well why not get a faster lens then? Well I do, I have a manual 135 2.8 I used for shooting my sisters' wedding, it was fast enough shooting at 800 iso (was shooting 800 iso all night), but.. 2 problems
1 I had to focus manually, as dark as the place was, it was a hit or miss with the 2.8 indoors, literally, I probably lost nearly HALF of my images from being out of focus, I don't know how many photos I took with that lens but I took 500 shots that night.
2 I could use my 55-200 VR still at 800 iso and not only did I have auto focusing so I never missed.. Besides the shot being taken slightly slower, having a shot with motion in it was much more worth it than an out of focus fast shot.
And for those that don't understand how much of a difference depth of field is with a 2.8, at the distances I was working at, if I missed the focus ring by 3mm or so from being on focus, the shot was pretty much worthless