I deleted a rant from this question because I felt it detracted from the given answer to the specific question. However, beamer is the "new kid on the block" in terms of giving talks (not that new!) and there are many little hints, tips, and howtos that people have found that can make the difference between a nice presentation and a smooth presentation - or make the difference between a downright annoying presentation and a nice presentation!
With the general idea that good communication is 90% of good mathematics, and also with a little bit of self-interest (I might learn something, and if not then hopefully everyone else's beamer talks will improve to the point that I can sit through them without wincing), I'd like to know what those hints and tips are.
These can be both technical (how to get the pauses right after an itemize/enumerate environment) and non-technical (the deleted rant was about not using loads of pauses just because you can).
Please be nice: say "I like it when the up-coming text is greyed out rather than invisible because I like to get a sense of where the talk's going" rather than "It's horrible when you can't read ahead because when the speaker is rambling then there's no way to work out what they're talking about".
Also, inevitably, there will be non-beamer-related stuff. That's fine.