If you've ever seen a live demo, you will know that these things are fraught with danger. Even if the wifi works, the presenter knows what they are doing, and nothing crashes, you'll often end up watching someone explaining something to their laptop in detail, or clearly demonstrating their inability to type. Either way, it doesn't make good, informative content, which is why I never ever demo in a conference talk - I'm there to entertain and time is always of the essence. At this point, you can probably guess why I'm writing a blog post about my screencasting toolchain - I simply pre-record whatever it is that I want to show in the talk.
On an ubuntu platform, I've had a few false starts with video over the years, and mostly avoided it. But now my "Debugging HTTP" talk really does make more sense if you can see the process of something broken, what the tools show, and how to understand that information and fix the problem.