I was at the fantastic Start Conference yesterday. I noticed something; for the first time, as many people were using iPhones when ignoring talks as were using laptops.
At tech conferences the geeks have their laptops open and are paying more attention to web surfing than to the speakers. At Start08, half those geeks (me included) were looking at their iPhones instead. In part that's because the Wifi didn't work very well. But also the iPhone is capable and more convenient than a big ol' computer.
One of the best uses of a laptop at a conference is participating in the IRC backchannel chat. iPhones don't do IRC (or do they now?) but we have an alternative: Twitter. Specifically, a Twitter search for a conference specific tag. I really enjoyed refreshing that page on my phone during a talk and seeing the commentary. It's also nice that the Twitter backchannel is persistent, non-anonymous, and archived.
I've always hated how many people at conferences (or in meetings) ignore the speaker and focus on their computers. Isn't the whole point to be together in person, to communicate face to face? But I get bored during talks too. The iPhone is a nice compromise; small enough to be discreet, limited enough capability to capture a bit of partial attention without drawing you in entirely.