Don’t put important information at the top of the screen if there’s header junk up there. I call this “the SMTP effect” since I think we’re trained to skip over the SMTP header garbage and look for where the real content begins (also relevant to banner ads, but they’re less subtle).
This Email unsubscribe form from HotWired is a good example. The damn text box for filling in your address blends into the ads and nav bar crap at the top. It’s even above the instructions! An otherwise handy form though.