I've made a few. No problems. They're really sharp if you use good source photos (which isn't too hard, it's pretty forgiving).
My advice would be to proofread and have someone else proofread it too. I forgot ONE family member's birthday on mine and felt so bad (it was a little kid's to make it worse!).
I haven't printed any calendars since the '08 upgrade, but I hear they do them bigger now, which can't be bad.
Any specific questions?