I thought I would like having the express card slot, but really the only reason I would have use it would be for eSata. Now with FW800 the point is really moot. BTW talking about the UMB, now is the UMBpro 13".
I know the speed of eSata is 375MBps, and FW800 is only 100MBps, but what do you have that transfers data faster than either of the 2? only if you have an external RAID cabnet. Why would you hook up an external RAID enclosure to a macbook pro? Isn't that what the Desktop is used for.
I personally would like having the SD slot, because my digicam uses SD. I like to sit on the couch, or lie in bed and import my photos for the day. It is a pain in the ass to hook up my cam, and have to make sure it doesn't come unplugged while importing.
Anyway back to the question at hand. I would use it for a data connect EVDO, or HSPA. I use an EVDO usb card at the present moment.