I guess it was just a lack of looking. There’s even a term for this approach, Suckerfish Dropdowns, although I’m not doing exactly what they recommend as far as IE support is concerned. However, I haven’t actually noticed it being necessary.
Now that may well be because I’m not even trying to support versions before IE 7, what with all of the transparent PNGs I’ve got everywhere. But still, the solution I’m using works great across all of the browsers I’ve tested: Firefox 2.x, Safari 2.x/3.x, and IE 7. The only complaint I have with it is that the positioning differs slightly between the browsers: the menus appear a few pixels higher in IE than in Firefox or Safari, such that they’re jammed up against the text of the menu header. But if I move them lower, the necessary contact (or really, probably overlap) between the menu header and the menu itself doesn’t happen… and if there’s a gap of even 1 pixel between the bottom of the header and the top of the menu, the menu will disappear if you don’t mouse over it fast enough.
Geez. I read a paragraph like that last one and I just have to ask myself, what am I doing with my life???