Gmail has a very annoying habit of adding people you email to the contacts list without your approval. This feature has been fiercely debated for pros and cons for quite some time. If you are asking for our opinion about this, then here goes, Gmail definitely should have this feature where they add contacts to the list but they should ask the user like Yahoo Mail does.
In Yahoo Mail when you email a unknown contact, you are prompted to authorize storing them in the contact list, quite unlike Gmail, which auto-adds the contact.
The Gmail team though, have picked up a cue here and there and have Gmail,Gmail Contacts,My Contacts,Suggested Contacts,Gmail Contacts Feature