I have one, and a few other color tools. I've found I rarely use them for picking fabric, but do use them for decorating.
The only time I find them really useful is if someone is picking out the colors and I need to match them up to the fabric, but I rarely make quilts for specific people so don't have to match their color scheme.
I've gotten a lot of good ideas for color combinations by looking at other quilts online, and if I find a color combo I like, I'll keep it in mind until I find a pattern that I think would work with it.