I can contribute some anecdata here. For about a decade now, I've made it a point to do some end-of-year giving to software projects I've found useful over the year, tracking down tipjars and paypal links and sometimes just emailing people to ask how I can say thanks.
I figure it this way: I'm using "free" software, but what if I wasn't? What would I spend on Windows licenses and apps and stuff over a year? I'll set aside that amount of money, and put it into the hands of those who deserve it.
In several cases, folks have asked me to give the cash to a charity instead, or find another project to support because they're doing alright and the words mean more than a few bucks.
Not only have I gotten some fantastically appreciative responses, but I also come away with a glowing pride and deep satisfaction myself.
Their commitment isn't thankless. My gratitude isn't silent. The feedback loop isn't broken, and the end-user's voice has been heard loud and clear.
It says "you're awesome".