Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
There is not any room left in the MB to allow for an Express Card, I haven't ever heard of anybody who would use one. And if you really need one, then get a MBP.
 
When I got my MacBook Pro I didn't even think about the Expresscard slot, but now I have a card reader for it, it saves so much time when I am out and taking photos, the download speed is so much faster than from the camera or a USB card reader.

You do realize that almost certainly the ExpressCard memory card reader in your machine is actually connecting via the USB 2.0 bus (USB bus support is part of the ExpressCard spec).
 
Actually my ExpressCard slot in the MBP is used quite nicely with a little $20 (refurb) card reader that I just keep in there -- the weight is like 30 g, so negligible to me, and I always have access to my memorystick pro duo with my little sony p&s. One less cable to fumble around with.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.