Ikke testet:
SELECT x.*
FROM POSTS x
JOIN (SELECT p.postid,
SUM(v.vote) AS points
FROM POSTS p
JOIN VOTES v ON v.postid = p.postid
GROUP BY p.postid) y ON y.postid = x.postid
ORDER BY (y.points - 1)/POW(((UNIX_TIMESTAMP(NOW()) - UNIX_TIMESTAMP(x.timestamp))/3600)+2, 1.5) DESC
LIMIT n