Comment 17 for bug 732653

 One of the things that I find particularly annoying about this auto-hide behavior is that it makes it hard to aim for a particular sub-menu. Essentially, you grab the mouse, hit the top of the screen, then slide along it until you hit what you want. Without auto-hide (IIRC this is how it works on OS X) you can see it the whole time, so you can aim for the target you want without slowing down or correcting course. My understanding of the motive for Apple's choice with these menus is that they are much easier to hit then the windows-style menus because they have an infinite effective depth (infinitely above the monitor). But if you cannot see the menu and you have to hit the top and then slide over, you have to slow down anyway to avoid hitting a neighboring menu. So you've lost much of what makes global menus great.

One almost tolerable workaround I have for this is to hold down the alt-key with my left hand as I reach for the mouse. That means that the menus are showing by the time I move the mouse to hit the top of the screen. Please add my vote to those wanting this feature to be tweak-able. In terms of specification, I would be happy to have it fully displace the current top level menu that show the application name / what page you are on when the delay is tweaked. Another possibility is to have an option where the global menu shows up as soon as the mouse starts to move rather than when it hits the top.