* Note: To use the current Gmail Contact Manager, you must have the new Gmail interface by using IE 7, Firefox 2 or 3, or Safari 3. For more info click here

 Auto Add of Contacts

  Each time you send,reply,or Forward Gmail will add the address to your contact list & it will not add address from any email that you received have not reply to.

here how you can delete unwanted contacts

To permanently delete a contact:

1. Select the contact in the Contacts list.
2. Click Delete Contact at the top of the page.
3. Click OK.

  This feature can not be turn off and this has been discuss many time. check some of these Discussions

   from the group. and this also been  Discussion every since day one of Gmail check some of these Past Discussions 

If you don't want to read through all the past discussions  go here to suggest it to gmail this is the only page for your vote will be counted through the suggestion page.

Gmail Suggestions Page