For speakers, I always wait until they gesture as it tends to add life to the photo.
I've also stood on the speakers platform, behind the speakers, with my UWA. Most of the time I'd be checking things out through the viewfinder but it doesn't hurt to occasionally try out the good old "Hail Mary" method of shooting over the speaker's head and/or shoulder to the audience. Something like that is a great for setting the scene and can be very dramatic.
For the audience, I would try to get reaction shots when the speaker says something profound and/or funny.
I always left it to one of my other photogs to cover the cocktail parties. I hated doing those things, and I was usually too busy drinking and smoozing.
Another thing I never did was take pictures of people eating. People look their absolute worst when they've got a fork in their mouth or they're chewing.
Conversely, if people are sitting at tables prior to the banquet, you can sometimes get some interesting interaction between people at the table. People also tend to love those "I was there" photos but, again, not while they're eating...and especially not when they're doing something potentially embarassing with someone who's not their wife or husband.
I also hate "grip and grin" shots but, if that's what the conference organizer wants, that's what he gets.
Good luck. Have fun. Drink a beer for me.