I just got my test prints back from WHCC, and a few people asked me to let them know how well the colors matched.
I sent my photos to WHCC after working on them on my uncalibrated MacBook Pro. I wish I would have sent some photos with better colors to test, but I just used my most recent photos. I took some photos, mainly to show the differences in before and after calibrating.
After shooting on white seamless, and adjusting in photoshop, I came out with a nice grey/white background on my uncalibrated monitor.
The 8x10 prints came back with a small amount of magenta tint.
I busted out my Pantone Huey calibrator to hopefully fix this:
Plug it in and start the program. First it measures the room light. Room light affects the way your photos look just as much as the monitor color profile, so make sure your in good light. The calibrator then looks at colors on your screen and corrects them.
Here is a shot to show the changes it made. While these photos will show up differently for every one of you, the calibration added the magenta that was missing. It also "dulls" many highlights/shadows as well as colors since printers cant achieve those extremes. I actually prefer the colors before the calibration for everything but photo editing, so I turn the profile back to normal whenever I'm not editing photos.
The left side is corrected and the right is uncorrected:
Here's a photo of my desk. The lighting is terrible:
Overall, for $20 it was well worth it. I think they normally sell for around $60. I think some people have had issues with using Pantone calibrators with Snow Leopard, so you might want to look into other brands.