The two types of people who cause the biggest grief in open source
sayspy.blogspot.com
sayspy.blogspot.com
I really don't like the "if you don't have a solution don't complain" approach; that just stops bringing people to the table. Many people in O/S who start off being complainers end up contributing; sure, others don't, but if you tell them to go away they won't just shut up, they will just tell their friends how crappy they think you are. Sure, you might not care about that, but I think a terse note to an FAQ covering their question is more constructive, and helps mitigate developer burnout a bit.
Now, I don't think the correct approach is to tell users to shut up. That's just dumb. I do think it's important to try to convey that there are real people working on this software, with real life pressures, and unconstructive criticism is not going to have any kind of positive result. At best it will have no effect, and at worst it will cause developers to lose motivation and move on.
One of the myths of open source software is that the whole community is pitching in, and developing software in tandem with a "core team" who is setting the direction for the project. The truth is that most of the work is being done by one or two developers, and the cumulative contributions by others in the community does not come close to what they're doing.
There are few open source projects that can survive if one of those core contributors becomes demotivated or loses interest.
Most people who work on open source software do so for the love of programming, and the joy in helping other people. When you read stuff like "This sucks!", or "I wasted so much time fighting with your project today", you start to question if you're really helping people. You think that maybe you should move onto something else that would help people, focus on a startup for yourself, take on contract work, learn something new or whatever. If you're like me, there's a dozen projects you could start on today if you weren't focused on an open source project.
You don't have to treat core contributors like rockstars, but it does help to treat them with respect and remember that there are real people behind those keyboards.
I can appreciate that you have some "demon customers" causing much grief in those two groups, but you also have the target users for your software giving you feedback on their own pain points. You don't want to lose their input, otherwise you're creating software that no one can use and tossing it into a hole.