It's certainly nice to have on a smaller laptop screen, but on today's big desktop display it's not really necessary. For me, it's mostly useful for programs such as Photoshop, Aperture, Logic, WMs etc. And Aperture already has a fullscreen mode for photos built in, which is enough for me, and VMWare's Fusion has it as well.
What I would like however, is a setting that would automatically hide and show the menu bar. That would free ups some space and be very useful at times. I had a plugin that did that in 10.5, but it stopped working in 10.6.