Using Ajax for the sake of Ajax

Breaking the back button

Not giving immediate visual cues for clicking widgets

Leaving offline people behind

Don’t make me wait for Ajax

Sending sensitive information in the clear

Assuming AJAX development is single platform development.

Too much code makes the browser slow

Not having a plan for those who do not enable or have JavaScript.

Inventing new UI conventions

Changing state with links (GET requests)

Blinking and changing parts of the page unexpectedly

Not using links I can pass to friends or bookmark

Not cascading local changes to other parts of the page

Asynchronously performing batch operations

Scrolling the page and making me lose my place