This can be done by clicking the label ("work/home/other") next to the desired email address, and choosing "Send Email."
- To send an email to one of your contacts, select the person's name in the contact list, click the label to the left of the email address to open the pop-up menu, and choose Send Email.
That is an interesting new feature that I didn't know about. However, in the time between my asking the question and your helpful answer, I actually discovered what I was REALLY looking for, that is when you are addressing a number of people and don't want to go into each card individually (because it would take too long) what you need to do is 1) write the email, then 2) go to the pull down menu under "window" and look for "address panel" That will open your "contact" within the mail program and all you must do is click the name, and then in the upper left hand corner click on "to," "cc," or "bcc." This is only one extra click you must perform is this new incarnation of the mail program. I don't know why they made it more complicated, but I suppose the world doesn't revolve around the likes of performing musicians like myself--although in a perfect world....
It's been like that since at least 10.6 and probably farther back, so i'm not sure what behavior you think has changed. If you don't want to go to the menu, though, you can just click the "silhoutte" icon in the mail composition window to get to the list of contacts:
Perhaps you were looking for the older button that looked like a book and didn't realize that the icon had changed but the function is still there?