That is an excellent question!
At this point in time we've been told that the r-pi will come with 16 GPIO 3v3 DC pins. They *might* choose to leave these unattached such that anyone who needs them can solder them on, but we'll have to wait for the official word on the final boards.
Now with a simple interface that means there's a lot of things we can do with these pins, but the real question is do you need analog signals, or do you just want digital signals? I was thinking about using the r-pi as the brains is a security system with read switches on the windows, and maybe a usb camera at each of the two doors. All of this would work fine with digital signals, but if you want analog you need to look for an analog to digital convertor to make it work.