Salesforce touts integration with Google Apps as one of their selling features (see Edition Comparison). But what you think is Integration may not be what Salesforce calls integration. (And no, this is not just Salesforce - have a look at Microsoft Dynamics CRM "Integration" with Sharepoint). 

Enabling the Google Apps Integration gives you this

• Attach Google Docs to Records
• Send Email (from Gmail). Sending Email from GMail does this: 

• • It opens Gmail and adds that person’s email to the sender, plus the standard BCC email for SF.
  • If you want to send to multiple people you have to add them manually.
• When the email is sent, the  Email is created as a Task in SF
  
  

• And as a chatter feed.
  

The external user replying to the email DOES NOT GET LOGGED IN SALESFORCE - you have to forward it to the bcc address when you receive it in your inbox.

Is this what you would call Integration? Also see my blog post all about Integrations http://thedetaildept.com.au/2013/09/15/integrations-are-the-new-black/