Dave's Dashter certainly does it right, prefilling a form that clearly indicates what will be sent and sending it. Kudos for that (and the very awesome Dashter too).

I do wish someone you come up with a chunk of code that ALL plugin authors not using the wp.org repo could use the check for update and auto-install. In fact I really think this should be in core, although I suspect the powers that be would strongly object to that. Having a system built into core would at least standardize the data policy surround updates and potentially around bug-reports too.

Aaron does raise a good point about data sharing between wp.org and Automattic... would be interested in learning the answer to that.