I don't really hold a grudge on this project but I can understand (to a certain extend) the people who do. If my memory serves me well, throughout the project they never mentioned that the founding engineer had left the company or any other of their most serious issues. The last status update was that they only needed UL certification and would be ready to ship the machines and then suddenly they reveal that the project is pure vaporware. Even after that, they promised an update 'in the next month' on fulfillment possibilities and it never came. The failure is excusable and was always a risk but the dishonesty and almost total lack of transparence makes the rancor of some backers very understandable.
The problem is people with more balanced views also have other things to focus on in their lives, so here you have it - even if most backers understood the risk they were taking and have no hard feelings, years later we only hear about that other small subset
My full take away from the situation was simply that they had bad business sense and burned through cash on a several bad decisions, then hoped to pull success from the jaws (or more realistically, the stomach) of defeat, so made ridiculously upbeat postings in an attempt to hand wave over the cracks in the project.
It was a risk; I took it on. Not my most expensive bad investment by far. I checked out of monitoring the Kickstarter feed once it became clear that it was going no where. That was well before the final gasps from the ZPM people.
I'm glad that Kickstarter has pushed projects to post risks, avoid renders, etc. None of that would have mitigated the bad-businesspeople issue, however.
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Edit: To make things clear, I really don't hold a grudge on this. I threw money at some clever ideas, but we all know making them happen at scale can be hard. They didn't handle things well but I felt that the hugely negative response was largely an overreaction.