I guess that having commented on the blog that answers would be better here than on the blog, I might as well open a question...

This question is designed to encourage us all to think about what we want to use a potential API for before making specific feature requests. Ideally, answers would be structured as:

I want to build...
... an Android widget which can show me my current rep, badges, and rep for the day, across multiple sites

For this, an ideal API would...

• Let me query multiple fields in a single request
• Let me specify multiple sites (with multiple user IDs) in a single request
• Access badge, rep, rep-per-day information

Other answers may well be much more detailed, of course, but hopefully this gives the gist of what I think might be a useful type of answer. Things like useful formats (JSON, XML) would be interesting to Jeff Atwood too, I'm sure.