Having been to many conferences over the last 10 years, one thing that I find myself (as a part of the audience) subjected to with depressing frequency is this scenario:
Chairman: "And our next speaker is Fred Nurk, who will be talking about Prestressed Bacon Yoghurt..."
[Nurk plugs in laptop; looks at projection screen.]
[Much fiddling and pressing of keys. Projection screen stays blank.]
[5 minutes later]
Nurk (weakly): "Has anyone got a USB stick?"
[A USB stick is found. The presentation is copied to it, and then onto someone else's machine. The talk starts, 10 minutes late.]
This isn't the only similar problem, and it's not limited to any given technology: Windows and Linux systems can both have technical problems with display switching; Some people just don't know what buttons to press; Mac users tend to forget to bring their special Apple-to-VGA dongles...
Now, I'll grant you that in many cases, there are peculiarities of the projector or the laptop that cause problems. It happens to all of us. However, I'd venture to suggest that it might be a good idea to try it out first, instead of holding up a roomful of people for 10 minutes while fixing it.
This behaviour is bad enough in a normal speaker, but I've seen it happen to a keynote speaker, too, this morning -- using the laptop supplied by the conference organisers for his plenary opening speech. If I was the conference organiser, I'd be rather embarrassed by that incident.
Now, since I learned how to use XRandR properly, I haven't had a problem with any of this, but even so, if I'm doing a talk, I always try to take a couple of minutes in the break before the session starts to plug my laptop into the projector and test it. If it doesn't work, I'll grab someone else who's going to be in the session -- or preferably someone who's already done one in the same room -- and arrange to use their machine instead. This isn't rocket science, people...