The main advantages for us is to free our own hardware of mail handling, to get better and more advanced statistics. (Mandrill) and to ensure our email is sent to our client and members inbox and not spam folder.
You reach a certain point that it is more cost efficient to outsource certain services, due to manpower and hardware costs, we reached that point when our outgoing emails passed 4000+ emails.
What is Amazon SES doing to deliver the mail right into the members inbox and not in their spam folder? Are microsoft, google etc. handling mail in a different way when mails are send from amazon servers?
I've just set up Amazon SES on http://speakev.com as I was using Google to send but finally broke their sends-per-day limit. I'd rather my web server didn't handle emails in part because of the strain (and time setting it up) and in part because I'd worry about being blacklisted if someone decided to report forum notifications as SPAM regularly.
So far using SES has been totally faultless, easy to set up and it "just works", seems very good value too.