In the Gmail Labs Class of 2010, six experimental features have graduated to become supported features and five have been expelled.

Google introduced Gmail Labs in June 2008 as a testing ground for experimental Gmail features, some of which Gmail product manager Keith Coleman acknowledged at the time might be bad ideas.

Gmail Labs began with 13 experiments: Quick Links, Superstars, Old Snakey, Pictures In Chat, Fixed Width Font, Custom Keyboard Shortcuts, Mouse Gestures, Signature Tweaks, Random Signature, Custom Date Formats, Muzzle, Hide Unread Counts, and Email Addict.

And it later reached 60, including features that range from useful, like Message Translation, to quirky amusements, like Mail Goggles, which requires users to prove their sobriety by solving a math problem before sending a message.

In a blog post, Google software engineer Mark Knichel explains that the decision about whether to keep or end an experiment depends upon how many people use it.

"Retiring features is always a tough decision -- we invest in building and maintaining them and we realize some of you are probably fans of some of Gmail's lesser-used features," he explains. "But Labs are experimental features, and from time to time they may break (that's why there's a quick way to disable them), or even disappear."

The six features that have become officially supported Gmail features include: Search Autocomplete, Go To Label, Forgotten Attachment Detector, YouTube Previews, Custom Label Colors, and Vacation Dates.

The five discontinued features, three of which have been with Gmail Labs since the beginning, include: Muzzle, Fixed Width Font, Email Addict, Location in Signature, and Random Signature.

According to Knichel, the retirement of these experiments will make room for new ones.