From my live tweet point of view there seem to be three types of speakers.
1. The speaker with a lot of ground to cover who flows on with no stops and speedy slides. All of the information is useful but it feels shapeless. It's hard to tweet these speakers without a real hook. Maybe spending so much time in a 140 character virtual world makes me value concise ideas more. Or it may be a signal to sit back and listen.
2. The speaker with so much great content that you can't possibly share as much of the knowledge as you wish you could. In a case like this you can only hope for more live tweeters in the audience fill in the gaps.
3. The rare person who makes a point concisely, elaborates on it, leaves his slides up long enough for you to absorb them and then, almost precisely at the same time as you press send starts on another great idea. I always wonder if those rare speakers are twitter natives. Could Twitter be changing our brains?
There must be more types of speakers than these. Please comment if any come to mind.
Here's an article about live tweeting scientific conferences: