The following article by Steven Faulkner over at The Paciello Group is essential reading for anyone writing HTML. It concerns the use of the title= attribute and it’s proper uses, as well as detailing some abuses. The title= attribute has not been fully supported or implemented in browsers consistently, and is even less useful for screen readers and mobile platforms.

HTML5 Accessibility Chops: title attribute use and abuse | The Paciello Group Blog.

The “Further Reading” links on that page are also essential reading, and the title attribute usage examples