Hey there B. -
I currently have the Mirena, had it placed in October 2007. Although I don't have a personal answer for your question about getting pregnant, after months of frustration with "symptoms" that were un-explainable, i.e. 27 lbs of weight gain in 10 months, chronic vulvar itching and dryness, NO sex drive, moodiness, bulging tummy, cramping, non-stop spotting, etc. and 3 visits to OB-GYN's complaining, only to be told that it is in my mind, that the Mirena does NOT cause these symptoms, I found this website that might help you:
http://curezone.com/forums/fm.asp?i=70147. Although I didn't read all 500+ responses, I did read a few that mentioned how long it took them to get pregnant after having their Mirena removed and quite a few that talked about their menstrual flow. It sounds like you are happy with your Mirena, so disregard those of us that have had adverse reactions to the hormones, but there is a lot of good info pertaining to your questions.
Best of luck!
C.