I think it will become increasingly common for people to be tapping away, (they could quite easily be taking notes on their mobile devices; I do this) so I think we will probably go from being distracted by it to not thinking of it as unusual.

Can’t say it bothered me, nor did I notice it much. The very nature of only having 140 characters mean it’s a quick thing to do, and most people only posted once or twice during any presentation.

In a way it validates that you are saying something interesting to others, and there is a whole other concept around the ‘back channel’ which now takes place in many technical conferences, of which Twitter is a part.

Also not sure I’d use the word ‘frantic’ as it’s no more or less noticeable than someone writing down some notes during your presentation and that happens a lot.