A better question is:  what is the best way for everyone to get as much value from the speaker as possible?

Specific to twitter, at least there is some data on the question. Over at Consumer Centric they’ve posted an analysis of live tweeting of a session. Here’s the summary (based on 686 tweets):

75% of all tweets quote the speaker
13.6% were alerting others where they were
6% arranged for meeting up to discuss something
5% praised the speaker
4.4% were random or off-topic

First off, it’s important to note this breakdown will change wildly depending on:

• How good the speaker is in keeping people’s positive attention
• The makeup of the audience and their interest in good will

As a speaker, the above seems like good numbers. Some of those tweets repeating what was said will hit people who aren’t in the room, effectively making the audience larger. Assuming they quote the speaker accurately, this makes the effective audience bigger.

But anyone who is staring into a laptop is not making eye contact with the speaker – they are taking a little bit of energy out of the room in order to give it to people who also have their eyes on laptops, either in the room or elsewhere. I’d rather have most people fully engaged on what I’m saying, and a few dedicated people live tweeting, then never being sure if people’s noses in laptops is a good sign or bad.

Read the rest of their post for a summary of kinds of tweets they found – if ever you choose to livetweet a session, there’s good advice here.