5
i had some good drop down menu's before i redesigned the theme on my old site.. i think the scripts are still on the server, if i can gain access to them.. but i don't work for that site anymore as i quit last year so i might not be able to.. it would just be a matter of editing the links then.. (altho these were horizontal drop downs using either click to drop down or onmouseover events)..
the problem with having too many is that your pages can become overwhelmed with javascript which will make page loading time suffer, which was 1 reason i took them off and went for simple point and click buttons instead..
if you're going down the route of drop downs then i'd recommend being a bit conservative as to how many you actually use (just an opinion)