This would not work for several reasons. First, Ubuntu is not designed to make money. The community is made up of volunteers. Trying to collect donations would get very tricky. The first issue would be, who would handle the money? Who who would decide how it is spent? What country would the money be kept in (which would affect the laws/regulations and taxes and other stuff like that)? Many people would probably also be against Ubuntu trying to collect donations in this way due to the Ubuntu promise stating "Ubuntu will always be free of charge, along with its regular enterprise releases and security updates". Although Ubuntu is still free, this idea would have it trying to earn money. I also have one last question, why do we need this money? We have a very large and growing community filled with people willing to work for free to improve Ubuntu. Adding money into the equation simply complicates things.