[Lynne]

You need to go do a search through your pages to see where this query is being used. Do a global search for something like "ISNULL(customavatar.userid) AS hascustomavatar" since it looks like a pretty specific thing that doesn't get used often.

edit: Yep, only 22 instances. It looks very much like the query in memberlist.php on line 562. Start with that, see if it's the same query and if there are additions to the query from the standard (like from the hook above it - memberlist_fetch).