Over the last few years, video has become more and more commonplace on the Web, usually using Flash (other plugins, Quicktime et al., seem to be fading into obscurity).
I absolutely bloody hate this. There’s a number of reasons; firstly, Flash is a proprietary format (as are almost all the other formats commonly used for video; the non-proprietary ones are still exceedingly rare). That means that if I’m to view these videos I’m at the mercy of the proprietary developer. In practice, that means I can’t view these videos on my desktop computer, as I run an operating system that Adobe choose not to bother supporting (FreeBSD). I’m not willing to stop using the operating system I prefer just to watch the occasional video.
Secondly, I’m impatient. I want to get the information at my own pace. I want to speed up if necessary, or slow down. This is easy in text; less so with video. At best, it’s inconvenient, and with streaming video it may not even be possible to skip forward. It’s often also difficult to find the exact point in the video you’re looking for; in a text, there’s almost certainly a Find function. (Related: I probably can’t watch a video at university or at work, even if it’s relevant to what I’m doing, if I don’t have headphones with me. If I need the information, I’d have to wait until I got home then do work-related stuff there — no, thanks.)
Thirdly, and while this doesn’t affect me personally, it most likely affects many more people than the other two: accessibility. If you’re relying on videos to promote your cause, you’re excluding blind people (if the visual content is important) and/or deaf people (if the audio content is important). A textual version, with images if necessary (and descriptions of the images if possible) is usable by both blind and deaf people (with a screen reader if necessary).
If it’s the presentation that matters — a work of art, for example — then by all means use video if that’s what you want to use. If it’s the content that matters, however, if you want people to buy your product, or become involved in your project, or support your cause, then by using video to the exclusion of more accessible formats, you are limiting your audience; how is that at all productive when you’re trying to promote something?
(An addendum: I’m not necessarily saying you shouldn’t use video at all, though I’d not mind. But you absolutely should provide an alternative version if at all possible, for people for whom video is problematic.)