Gmail Labs, the experimental Gmail playground in which every Google engineer can write a Gmail feature, sometimes retires features that aren’t used very much, and graduates commonly used features, turning them into regular Gmail features.
Today, Gmail has retired five features and graduated six others; over the next couple of days, you’ll see the retired features disappear from the Labs. I haven’t really used any of the retired features; if you’ve used any of them and are sorry to see them go, please share it in the comments.
The six Labs features that graduated are:
1. Search Autocomplete
2. Go To Label
3. Forgotten Attachment Detector
4. YouTube Previews
5. Custom Label Colors
6. Vacation Dates
The five features that were retired are:

1. Muzzle
2. Fixed Width Font
3. Email Addict
4. Location in Signature
5. Random Signature

The features that graduated from Labs are either no-brainers, such as autocomplete for Gmail’s search and previews of YouTube videos in e-mails, or nifty little details, like the Forgotten Attachment Detector which alerts you if you wrote “I’ve attached” in your message but haven’t actually attached a file to it.