Just a quick suggestion here, based on my recent experiences dealing with
a web server struggling under heavy load:
It seems to me that it is be very useful to know whether temporary
tables are being created on disk or in memory. Would it be possible to
change the current "Copying to tmp table" State message to read either
"Copying to tmp table on disk" or "Copying to tmp table in memory"?
If I have overlooked some other easy way to spot this info on a per-query
basis, I'm sorry. I know there are extended-status variables for this, but
being able to see it right on the processlist would be nice.