Jokes or not, I can’t concentrate very hard for more than 10-15 minutes at a time. The best presentations, I think, are the ones that take this into account and allow room for questions or some kind of interaction frequently. Also, not going too fast and not taking more than your alloted amount of time. I understand it is hard to cut information, but just keep reciting to yourself, quality not quantity. I’ll get much more out of a presentation that is easy to follow cause the speaker is speaking clearly and evenly, and I don’t feel like I’m just there to unscrew my skull to let you overpour facts into my skull.
Also, there is a difference between jokes and personality. Things like not being (noticeably) too nervous, speaking in plain language and only using jargon appropriate for the crowd (conservatively), talking like the presentation is just like having a conversation with someone at their desk, coming off as approachable all keep me engaged.
Now I just have to keep this in mind for my presentations :-).