I've never bought the Humble Indie Bundle. **shrug** I'm not that into Indie games.
However, I have done other "pay what you want" deals - mostly at DrivethruRPG.com for tabletop PDFs.
One time, I'd pledged to a Kickstarter and was going to get the PDF for free, but I had to wait six months for the rest of the Kickstarter stuff to be release. Rather than wait, when the PDF came up on a "pay what you want" sale, I paid a dollar. Thus I paid a dollar for something I was already getting free so that I could get it early.
Another time, I paid a dollar for a PDF there - but I'd never heard of the company or product before, so it was a sort of "let's see if this is good - if it is, I might buy their other products" sort of situation.
Of course, both of these deals were for a single pdf document rather than for a bundle of games. I've paid a dollar for a game before, but it was on sale for that much and not a pay-what-you-want situation.
... so yeah... this seemed more relevant when I started writing than it does now. **shrug**