First, I didn't vote in the poll since I'm using Snow Leopard, and the Full-Screen mode that most app's use in Snow Leopard is different than ML's official implementation.
If I did have ML, I don't think I would use it.
1) Since ML's Full-Screen mode creates it's own Desktop, going to Full-Screen mode would mess up the order of the Desktops. One of the reasons I'm still with SL is that I prefer the fixed grid of Spaces in SL. So that I don't have to hunt where a usually open app is. I know that Itunes is alway in the top right Space in a 3X3 grid.
2) Also I have 2 monitors, and using ML's Full-Screen mode kills the 2nd monitor. One of my main uses of Full-Screen mode in SL is having a video player on my 2nd monitor in Full-Screen mode. In SL, and from what I hear a few video players that don't use ML's official Full-Screen mode, this leaves the first monitor with the menu and free to do other things.