I bought mine last weekend after preordering and they didn´t have any extra in stock. They did get a new shipment last monday. Just call them and make a reservation.
I´m actually a little bit disappointed with this set. I don`t like the "sleepy eyes" look of Homer, Marge and Bart. IMHO the best minifigs are Maggie and Ned. Also the doll-/playhouse look of the set is bothering me, i really would prefer a more modular build. And the most annoying thing for me are the small windows in the bedrooms. The bed in the master bedroom covers the window.
Oh, and I almost forgot the roofless car :(