My 2011 13in (i5/4GB/120GB), I get about 6-7 with normal stuff (low-to-mid brightness, web browsing, lowest keyboard lighting, etc). I've tested in a couple times too, so this is a pretty accurate average for me.
I agree that the USB card will suck some of the battery life down. I get about 6-7 hours of normal use with light web browsing and general use. I don't have Flash installed so that helps a lot as well.