Hardware:
iMac 2.0 with Radeon 9600
Canon i960
Software/OS:
OS X 10.4.3
Aperture
Anything else that prints pix in OS X.
I am fighting with my Canon i960 to get it to print pix anywhere close to what I see on screen.

Now that I'm playing around in Aperture I'm playing around with people pix much more often so I'm really noticing the colour issues, but it's an issue with my printing in OS X in general, not just Aperture. Mind you I get less options in other apps, so it's harder to overtweak with those.
I know this is not ideal, but the only colour calibration I have done with the iMac is the built-in colour calibration tool in the system preferences. However, whether I use the default iMac calibration or my own iMac calibration the Canon default colours are still way off.
If I use the Canon ICC profiles in Aperture, everything is really bad. If I let Aperture manage things it's closer. In fact, it's the most close if I use Canon's Photo Paper Plus Glossy paper (with the appropriate setting) while letting Aperture control the ColorSync Profile, but if I use Photo Paper Pro (with the appropriate setting) things are way off again. Dammit.
By the way, in Aperture's ColorSync Profile options for printing, what does "System Managed" mean? LIke I said, with one type of paper it gives me the closest results. As soon as I use a Canon ICC profile, things get very screwed up.