Design Guidelines: Tabs

In a series of Design Guidelines I will start by looking at tabs.
Tabs are one of the few elements found in real life that has enjoyed significant success on line. Amazon set the standard for years, until recently their product range became too big to fit into one simple row of tabs.
When using tabs in your web application keep the following in mind:

• Limit amount of tabs. Absolute maximum should be 7.
• In linear navigation (set-up process, registration) don’t use tabs.
• Keep the real life metaphor of tabs in mind when designing them.
• Steer away from more than one set of tabs. If needed, ensure that set 2 (child) has a distinct visual difference from set 1(parent). Avoid a 3rd set of tabs.
• Keep it short. The number of words on a tab should be less than two.
• Current(selected) tabs should looks visually different.
• Don’t mix horizontal and vertical tabs. This creates confusion.

Notes:
Because your have so little space available on a tab it can be hard to choose the right word description on a tab. It might worth it to look at some other way of navigation.

Amazon tab usage:

Yahoo tab usage:

Hopefully these come in handy, feel free to add more guidelines in the comments.