I went to Pycon last month (my first conference ever!) The conference was totally awesome and I met a lot of cool people. But I was also pretty appalled at the question asking at the end of each talk. Here's some stuff you should keep in mind before you ask a question at a conference.
Ask questions that you believe would be relevant to at least a third of the people in the room. Otherwise, avoid the temptation to show off your specialized knowledge to the room and just ask the speaker afterwards. Most of them are approachable on Twitter, email, or just in the hallways.
Ask only one question. If you have more than one question, pick the best and ask the other one in private later. Or ask your first question and then go to the back of the line. Other people have questions to ask as well and may not get to ask one.
Avoid buzzword bingo. It feels like lots of people walk up to the microphone just so the room can hear them mention some buzzword that indicates they know something about the topic. If I am running a Scrum team should I use Soak testing? How does Node.js influence the development of the PyPy project? If you wouldn't ask the question without a room full of people present, then don't ask.
Ask a question, don't make a comment. Talk time is for the speaker to be the expert, not you. Write up your comment as a blog post and post it for everyone to read later.
Be brief. After a talk, time is precious and many people may have questions for the speaker, so don't ramble about how nice it is to finally see the speaker in person, or how enlightening the talk is, even if those things are true. It's a matter of courtesy to everyone else in the room.
There is an easy solution to bad questions that no one has bothered to implement yet. Have people submit questions anonymously and have the speaker or a moderator choose which ones to answer, or have the room vote using a tool like Google Moderator. This will solve the problem of the question asker-bragger asking a trivial question.
The other solution is to charge money to ask a question, which could go to whatever cause you want. If enough people in the room have the same question they can contribute to the fee to ask the question and have it asked.
Update: There's some good discussion on Hacker News. "If the question you're asking makes you look smart, there's a good chance you're being a douchebag."
Also my friend Alan Shreve wants to know if it's appropriate to push back if the speaker dodges your question.