I've been there in June. Check out the Bermuda Kitesurfing Association at http://www.bka.bm/index.asp
for info on locations and weather.
Also, windguru has some info: http://www.windguru.cz/int/index.php?sc=32728&wj=knots&odh=3&doh=22&go=1
Simon runs the kite school at the 9 Beaches resort; see http://www.surfshack.bm
. Contact him at firstname.lastname@example.org
; he's a great guy and really helpful!