I reviewed more than a dozen color correction plugins some time ago. Intellihance was in the lower middle field. The best and fastest corrections were achieved by ColorWasher (http://thepluginsite.com/products/photowiz/
) and iCorrect (http://www.picto.com/
Intellihance is too expensive and a bit inconvenient to use. My impression is that it has been developed at a time when digital photos were not very common, because it doesn't work that good on color casts that are typical for digital photos. If you still use an analog camera and scan your photos, you will achieve better results with Intellihance.
The brightness and contrast features of Intellihance are quite good and very similar to ColorWasher. Intellihance's Sharpeness feature is a bit better than the usual Unsharp Mask filters.
Intellihance has a lot of different correction functions under one hood, but most of them are only middle class. If you don't need all of these features in one place, you can find cheaper and better alternative tools for them.