Being a Yahoo, I win the ability to suffer through both Vanguard's and Fidelity's online money management websites. This post is not to gripe about those, though. This is simpler. You see, I couldn't figure out how to log out of the Vanguard site.
As illustrated at right, Vanguard does provide a logout link on every page at the top right corner but its colors, being fairly similar to the browser chrome and pretty low contrast, prevented me from noticing.
Fidelity, for all its flaws, has a bright lime green header that makes it impossible to mistake for anything but the most awful of Firefox themes. The logout button there was easy to track down.
The lesson here? If you tuck important stuff too close to the browser chrome and don't differentiate it from said chrome, no one will see it. I know many designers that design websites without the context of a browser window surrounding it. Better is to design your site to jump out from the browser window so that everything is noticed according to its importance.