Q: Is VR important?
A: VR is really handy, under certain circumstances. Also, the VR versions of two popular zoom lenses, the 55-200 and 70-300, are generally regarded as superior all-around.
VR stands for "Vibration Reduction." Basically, it shakes the lens in such a way as to counteract camera shake. It's important to understand that while VR will allow you to shoot at slower shutter speeds without blurring from shake, it does not freeze subject motion or permit shallower depth of field, as will a lens with a faster aperture. Unfortunately, fast lenses are usually very expensive, unless you go for old manual focus versions, or third-party manufacturers like Sigma and Tamron. (Note: Sigma's version of VR is "OS," for "Optical Stabilization."
If you mainly shoot using a tripod, VR won't do you any good; if you shoot handheld or with a monopod, especially at telephoto lengths (200, 300, or longer), VR can be a lot of help, although it's not a panacea.
One thing to bear in mind is that if you're comparing two versions of a lens, one with VR, one without, remember that there are often other differences between the models as well. In the case of Nikon's 55-200 and 70-300, the VR versions are generally considered superior all-around, and not only because they have VR.
Note: Nikon currently has two version of VR, "VR I" and "VR II". VR I (used in the 55-200) compensates for about 1-2 stops worth of camera shake (i.e., instead of having to shoot at 1/200 with the 55-200, you could shoot at 1/100 or 1/50). VR II (used in the 70-300) compensates for 2-3 stops.
Nikon calls it Vibration Reduction (VR), Canon calls it Image Stabilizer (IS) and Sigma calls it Optical Stabilizer (OS). They all mean the exact same thing.
