Chris,
great point about the auto-playing. I can't stand it when music or video suddenly starts up on its own. And sometimes that happens by accident. The embed code we're given from some video sites is set to auto-play, so when we include such content we have to make sure we adjust the code accordingly. My friend Steve (@artfuldodga) made a good comment on Twitter about Flash elements "stealing focus." What he means is that if you are happily reading a blog entry, then a video suddenly starts playing on it's own, you are distracted from what you were doing and have to look elsewhere on the page to see what's happening. If you want people to read your content, you certainly don't want to disrupt them in the process. Instead let them click the play button when/if they are ready.

David,
That's so true, what clients think they want isn't always what's best for them. It's very easy to be charmed by a beautiful Flash site. And if you are simply admiring it, rather than experiencing it as a real user trying to learn more about the product or service, it will appear to be much better than it really is. If a client doesn't have experience with usability they won't know where the problems lie, so it's important to educate them as much as possible, so that Flash is used only in the proper context and only when it is the best tool for the job.

Brian
Exactly, if and when we use Flash, we always need to provide some sort of alternative, be that an HTML equivalent site or just sufficient alt text for a Flash element used within a page.