http://www.ncbi.nlm.nih.gov/pubmed/7665025
"CONCLUSION: This study shows that a 20-minute lecture was equal to the classic 50-minute lecture in terms of information retained by residents. If future studies confirm this study's findings, medical educators will need to reevaluate the length of lectures to improve efficiency of teaching."
So even more reason to limit the length of time given to people to talk.
In fact, if you're planning a talk, first do a 5/6minute version with fixed slides. You'll be forced to really think about what you want to say.
Then start adding what you think might still be needed. It probably won't be as much as you thought. What might otherwise have been a sluggish 45 or 60 minute talk is instead a tight 20-minute gem.
I was fortunate to be part of the MoutainWest RubyConf advisory team last year, and was one of the people pushing for shorter talks. I'd much rather see more topics presented in 20 or 30-minutes sprints than the usual 45 or 60 minute talk.
There are so many ways to get information out to people that you really don't need to explain it all in one shot. People start tuning out anyway.
Cover the essential concepts, point out some striking features, give a fast demo, drop the stand-up comedy patter, give URLs for more info. Then make your self available for questions later.
"Omit all the needless words, lexical expressions and verbage that are not required and so can be removed."
Or such.