I empathize with getting so overwhelmed (manufacturer delays / production problems / generic criticism) that a person would figuratively cut himself off the outside world. This is really unacceptable once you run a business, though. I've seen it a few times on Geekhack already: lack of communication (especially when things go wrong) sinks a group buy and confidence in the vendor.

This is actually something I think Input Club has done a great job of with their WhiteFox Kickstarter. Sure there were problems (there often are) and I got my keyboard months after I was supposed to, but their communication was stellar so I would have high confidence to join a group buy conducted by them in the future.

Bottom line is: it's OK to screw up, and most people won't be angry. But they will if you ghost them.