MySQL Query to get "Top 25 Posters in last 3 months"

[Eikinskjaldi]

SELECT u.*, count(*) as 'total' from user u
JOIN post p USING (userid)
WHERE to_days(now()) - to_days(from_unixtime(p.dateline)) <= 90
GROUP BY u.userid
ORDER BY total desc
limit 25

This will be a relatively server intensive query, I wouldn't run it too often.