I use Comet... I have glass sliding doors and they just get fogged with soap scum! All I do is rub over them with a wet sponge and some comet until they're covered, then I let it sit for about 15 minutes, then I wet it and squeegee it off. Absolutely no scrubbing needed! It works great for my tub, too, just sponge it off... even the chrome faucet comes out looking like a mirror! Just make sure you rub it with a dry cloth.
I haven't tried the eraser yet, though, so it may be just as good :)
Hope it helps!
Lynette