Do you calibrate your monitor?

Or do you? I just got some pages back from Costco and the pictures are much darker than they looked on my screen - the paper parts look ok (though still darker than my screen) so I'm guessing its my screen. Hmmm -actually, now that I look at these - the white edges are kind of gray, so maybe part of it is Costco. GRRR

I calibrate my monitor using the Gretag McBeth EyeOne (at least I think that's what it's called). It made a huge difference in the quality of my prints.

I use the ColorVision Spyder. At Costco, I have had to watch out to make sure that you don't let them color correct your photos. But, although I am happy most of the time, there have been times when the color is just plain ol' off somehow. Like the whites not really white.