Even if you manage to get it working, you have the 500 messages/day limit and the messages are all sent from the one email account, not from the original sender (both these issues are listed on http://docs.moodle.org/24/en/Email_setup_gmail)
Instead of using Google for SMTP I recommend using a service such as Critsend. It's not free, but incredibly cheap (and you get 50,000 mails for free to start you off). It will take you about 5 minutes to get Moodle setup to use critsend, and you get useful reports and statistics too (e.g. how many users open the emails sent).
We've used them for 2 years now, sent about 500,000 emails and not had any problems.