Try this. Is it just my 10.5.3 install or universal?
Open Address Book. Tuck it into the upper left corner of your screen. Adjust the bottom of the app to some measurable point (say even with the bottom of another open app).
Now close Address Book and do it again.
Again.
And again.
While the bottom of Address Book stays where you put it, the top edge of the app keeps moving down. If you're really bored and do it enough, only a few inches of the Address Book app will be showing.
I only noticed b/c I keep my windows adjusted to specific sizes. I know others are anal that way, too.