I have it on right now, but am thinking of turning it off. Everytime my wallpaper changes and I come back to wake it up, the menu bar keeps the previous wallpaper background behind it.
No. Opaque. Otherwise, it changes between apps, and is distracting when doing any graphics or imaging work. Even Aperture overrode it with an opaque bar (back before there was an option to disable the transparent one).
I think I've used the translucent menu bar ever since I found out I could years ago. I never have any problems with it, like old wallpapers showing up behind it. I think it nice to have it look more like an overlay than a solid bar. 🙂