The title pretty much says it all. Is it appropriate to ask a question for a minimal working example of some over-arching concept? (My specific case would be to put a title on a
beamerposter, for instance.)
In my opinion the general answer is: no.
The problem with such questions is that they obviously do not show any research effort, which is a must-have for a question suitable to the StackExchange network.
You can start making the example yourself (usually there is one in the manual), and you can ask about the specific issues you stumble across.
For a moment i was confused as percusse was and hence upvoted your Q later after reading twice.
My view point :
May be title should be rephrased as "Is it appropriate to ask for MWE by OP in his Question ?", just guessing to make title capture the message.
Specific Issue and Solution:
Your healthy attitude (to avoid being this guy) is greatly appreciated, but unfortunately there exist many beamerposter example and templates in internet as tohecz mentioned which is a part of research effort before posing Q.
Nevertheless,you can always ask for MWE on specific 'poster title' issue and mention clearly in question to avoid the full answer and effort.
Remember one should not recycle this MWE to post another Q without any significant improvement in old MWE code.
General Issue and Solution:
For a newbie OP, an MWE answer might not suit well( may have exceptions) because even if MWE was requested by OP newbie over time it becomes a full answer due to the number of comments below answer. your question becomes trivial as it defeats the purpose of MWE.
For a intermediate/advanced OP, an MWE answer might suit well(may have exceptions) because he just needs nuts and bolts with toolbox to build the full answer by himself
Answerer view point:
In any case MWE(submitted by OP) are best suited to diagnose the errors and get faster answers. But making just MWE in an answer does not satisfy the appetite of everyday learners/experts, hence they would go straight ahead to make full answer.
Short Answer: Yes, OP can ask for MWE, but OP may get more than what he wants due to highly patient and friendly people here.