If you are developing Open Data applications, best to keep in mind the growing mobile market. While you may think your clients are still sitting behind desktop machines or balancing laptops on their knees, there may also be lots of data hungry mobile users who should not be neglected.
What makes an open data site special, desirable, and impressive? How relevant and useful are the data? Clearly identified and well documented? Up-to-date? Unless data are meant to be stagnant (e.g. for research), typical users want data to be very current. But are there “typical” users? Are there “best” open data formats?