Comment Gmail has started to roll this out too. (Score 1) 240
Starting this past May or so, many Gmail users received a new "Attach Money" option that lets them send money through a Gmail email. It's integrated with their Google Wallet, which stores credit card info and uses that for payment. You can see more details at:
https://support.google.com/mail/answer/3141103?hl=en
I saw the "attach money" option appear just last month for me, while composing a new email. It seems a lot more convenient than registering for a new Square account and using their strange "subject and cc" method. I'd expect the Gmail version to be much more likely to catch on than this Square one.