If a have a question concerning interaction design, and I want to illustrate with a live example - e.g. a quick prototype hosted on http://jsfiddle.net, would that be okay?
Live examples are extremely helpful, it immediately presents the context of your application or question and may give details you did not or could not give in the wording of your question. At the very least give a screenshot if possible.
Screencasts are similarly helpful as you could point out the exact problem, though I suspect they could fall prey to the "tl;dr" problem. If you have a specific behavior in an application you want to ask about and JSFiddle can't handle a mockup of your app it's a good visual way to present the issue.