I have a Canon Pixma MX870 and I downloaded and installed drivers from Canon's site.
I've got it configured on two other macs in my house and it works fine.
When I tried to add the printer using the standard OS X on a new MBP, the preferences app doesn't automatically see the printer. I have added it via IP address and manually chosen the appropriate drivers.
So, the first question is -- why didn't the mac see it properly?
When I try to print, the job shows up in the local print queue, but then shows a message saying that "the printer is busy". I can printer from the other computers on my network without problem.
The second question is -- what can I do about the "the printer is busy" message? (I suspect if I resolve the first problem, this one will be a non-issue).
For what it's worth, I configured the printer on the other computers when they were running 10.6 (Snow Leopard), the new laptop is running 10.7 (Lion).