The Gmail development team is surely on fire for the past week. Another new Gmail lab feature was added on the weekend: “Suggest more recipients”.
Gmail will smartly remember recipients that you grouped in the past and can suggest them to be added to your email when it detects the same group of people already in your recipient list.
Sending junk *ahem* I mean, important emails to your co-workers or friends can never be easier than this. Never again create different recipient groups for different purposes.