[fury]

I made a query that does it. (counting how many posts contain each smilie)

select count(postid) as count,smilie.smilietext from post,smilie where post.pagetext like concat("%",smilie.smilietext,"%") group by smilie.smilietext order by count;

Warning, this query can take a few minutes and may cause your server to stop responding. Don't run it from phpMyAdmin.

It could possibly be run like once a week or so and the results put in its own table (but it would require being able to disable the exec time limit on a per-file basis) which could then be called in a fraction of a second each time the page is displayed