It grew on me as well - or at least I stopped hating it and started thinking it was decent, when I made friends with the mother of a baby Matison my daughter's age. (Pronounced like
Madison) I don't like Madi either, but I guess it can't be avoided, and it's not awful.
Madison has been less used than
Melissa,
Heather,
Jennifer,
Jessica, and
Amy were. It'll probably seem overused about at the same level as
Lori,
Megan, or
Hannah.
http://www.behindthename.com/top/search.php?terms=madison+hannah+lori+meganIt won't be more dated than those got, either - not as dated as
Brittany, which pretty much pegs a woman's birth as being within 5 years of 1990.
Congrats on the grandchild.