HI guys,
I've been working on specifying the data format for sending browser usage data to the server for analysis (see
http://wiki.mozilla.org/Browser_Metrics). The major goal for the data format was to make it compact -- we shouldn't hog the user's bandwidth to upload data. Originally we'd been thinking that a binary format would be the most space-efficient, but it turns out that XML data actually compresses very well with bzip2, plus it's highly readable, which should make it easy for anyone who is interested to see exactly what we're sending.
I wrote up an XML syntax for this, based on the events I've had a chance to think about collecting so far. I don't have any spec-writing experience, so I'm sure this is missing some details, but I think it gives a pretty clear picture of what I have in mind.
--
-Brian