You guys made this open-source, and free to use. I'm sure many people would donate to help keep you guys going.
I doubt that. Relying on donations would jeopardise the longevity of this project/product. It's not a steady income and that is what the developers need, an income which puts food on the table and keeps them at their computers writing code and giving us a software that will mature into something great.
Donations would not cover the operating/living expenses of the developers for to long. At least thats how the bear mind works. I give you guys something nice, you come give me a few fishies, but until there is a problem I might not get more fishes. I might not even get fishies again until I give you something else new.
Thank you for your feedback, I am glad you like the software enough to want to use it. I am sure in due time you will. Free or not.
Well, if XenForo had big sponsors like AOL or Google to start with and collection of ad revenues from customers' sites [would you agree for such a setup?], then I am all for it. Mozilla FireFox had $2 million donation from AOL. Not a bad injection for a non-profit enterprise. Now Mozilla collects $60-70 annually from search royalties.
If all you're looking for is a basic forum there are plenty of free alternatives, but if you need more than just the basics then you should expect it to come at an additional cost.