For what it's worth, I've learned to ignore the calibration warnings. Perhaps it's because most of my photographs are landscape images where color accuracy is a bit less important than for fashion or product shots, but I tend to re-calibrate only when I'm profiling a new paper.
I love the Z3100 overall, and it's been perfect for my needs. But it's fair to say that the driver (at least for Windows) is squirrely as hell, with lots of minor "issues". It tends to forget your custom paper sizes unless you reload them; it keeps screwing up landscape/portrait orientation; and the calibration reminder seems to be on constantly.
Yep. Great printer; crappy software.