But my point isn't who-invented-it, it's that it's very easy to implement this in your own buttons without using Bootstrap. I still use my own implementation, despite suggesting it to them. Just create some data attributes (I have data-default-message, data-inflight-message, and data-success-message) and change your buttons appropriately. I have a standard function that I call on my forms that handles that for me, which I've gisted here: https://gist.github.com/pamelafox/5714109 You could do that in a more elegant way than that bit of code. :-)
I prefer the changing-message approach to the showing-the-indicator approach because the verb stays, and you remember what it was that you were doing. Handy for us forgetful folks. You can use both, too, of course.