Maybe a good rule for presenters would be to imagine what happens if they replace the photo of girls in bikinis with a photo of guys in bikinis. If that makes the presentation awkward, then bikinis are not the answer.
Make it equal opportunity - scantily clad girls on left half of the slide and scantily clad guys on the right half. Then everyone's happy - straight girls, straight guys, gay girls, gay guys. Win-Win.