I bought the non IS
version six moths ago... and, to be honest, I am very very satisfied with it!!!!
Of course, IS
is helpful, but not mandatory!
In some cases you might think that with IS
you would have got a better picture, but, for me, they've been a few.
As many of our fellows have stated above... it depends on what kind of photos you are going to take.
Without a doubt, it helps a lot when panning... but, to be honest, if you have a still hand, you can take good pictures also at 1/80s. If mounted on a monopod or on a tripod, you may use slower shutters, but actually, I can't tell you anything about this, because I have tried it only hand held...
I think you won't regret the purchase and you'll relize what I mean when you'll have some trials at different zoom ranges and apertures!