Aside from the GUI requirement, I think that pretty much nails it. At least for myself, I envision this thing being a headless, disconnected entity that does its sensing autonomously, and the user retrieves the data by grabbing the SD card.
I think a solid, reusable library for reading and writing to SD cards is what's really lacking, right now. There are a few floating around, but nothing's really been well-packaged for use on the Arduino. Now that the 328 is available, I think that should be a relatively straightforward endeavor.