If you're worried about security and want to give your Google accounts some extra padding; that is, you want to have a backup email address associated with your account just in case, you can now do so. Google Groups Guide 2 has written in Google Groups about how it's done:
To add an email address to a Google Account, follow the link below and add an additional email to the account listed under "Google account". If you want to add an email to another Google Account, simply select "change account".
To do so, go to https://www.google.com/accounts/AddNonGmailAlternate.
Forum discussion continues at Google Groups.

Comments:
RICKI L
10/17/2009 10:00 am
IF SOMEONE SENDS A FRIEND'S EMAIL, HOW CAN I JUST CLICK ON IT TO ADD TO MY CONTACTS?
Delhanks
03/30/2012 01:58 am
How can I set up a group mailing and add members to it. Thanks del