I'm going to give this living hinges thing idea one more go because it just got archived. As a designer who regularly has to single piece objects with "living hinges" - thin plastic part between a box lid and bottom for example - it would be very helpful if the there was the ability to model this and have it function as a joint.
Right now it is simply not possible to go from design to mold with a testable closing box. This is a big part of desinging most things plastic injection molded.
This would also be highly useful for modling things like cips that fasten things close etc. Last time this got archived after 8 votes. I don't know how many it takes to rate implementation but I really hope this time it makes it.