[rake]

It'll be a little more complicated than showing the overall top ten.

Firs you need the time interval...
$searchdate = time() - 24 * 60 * 60;

then the query:
SELECT post.*, COUNT(userid) AS count FROM post WHERE dateline>$searchdate GROUP BY userid ORDER BY count DESC LIMIT 10

You'll get userame, id, and count will be the number of posts made in the last 24 hours.