Particularly handy if you are sent an email and want to capture the list of email addresses.

• click "show details"
• select the list of email addresses by "scooping" with the mouse (carefully positioning the mouse at the starting point, holding down the left button, moving to the ending point, releasing the left mouse button, and type Control-C). Make sure you get just the list of addresses and not stuff around it.
• click "Contacts"
• click "Groups"
• click "Create group"
• supply a "Group Name"
• paste the addresses in the "Add contacts" box
• click "Create Group"

Almost too easy. Neat thing about the method is that if GMail sent it to you, they will accept it in the "Add contacts" box.