I must disagree here. Too high a top tube can indeed be an issue. I recently sold a lovely bike whose top tube actually grazed my crotch when standing over it (turns out the frame I bought on ebay was one size larger than I thought), and I did have occasion to come down HARD on that top tube at least once. It was NOT pleasant! :eek:
And a top tube that I can't stand over at all (requiring tilting the bike to mount) would just be downright unsafe to me when mounting or dismounting the bike, and especially quick stops with cars nearby. YMMV, but there are too many bikes out there with appropriate standover to settle for one that is too high for you (too low may not exist, and if that is what celerystalksme is referring to, then ignore all of the above!! :o)

