To listen well, is as powerful a means of influence as to talk well, and is as essential to all true conversation.- Chinese Proverb
Social media is good and fun... but what are you doing with the conversations you're having? Jeff Hurt's post on "why your event needs to increase social media monitoring" is dead right!
If you used social media during your last similar event, the data to be mined is almost limitless. You can see trending topics, audience segments, gaps in engagement, and most importantly: tone of the conversation.
If your events are put on for the benefit of your customers or users (like training or advisory events), creating a listening channel to gather feedback and input for the agenda is a highly valuable and appreciated way to engage with your constituents.
If your event is marketing/sales-driven and you aren't seeking input from attendees, having conversations with them during and after the event is very important to shape your future experiences. If you actually do not care what your customers think at all about your event or your content, well then you probably won't have a whole lot of them next year. :-)
Onsite, there are a number of innovative ways to connect with your attendees via social media. You can create and publicize a specific hashtag for event help and have a group of event volunteers monitoring the feed and working to answer questions or solve customer dilemmas. If you have a customized mobile app, you can add a virtual helpdesk or other mechanism for requesting assistance. In your app, you can push real-time feedback surveys to ask about specific event elements, as well as get session feedback through the app. If you just want to pretend you're high tech, but don't really have the money to BE high tech, you can set up QR codes throughout your event which link to a simple form or survey. When scanned with a smartphone's QR reader, the form would open allowing the attendee to put in a question or answer a question (depending on what you are trying to accomplish).
Customers are more and more annoyed at companies that don't listen. If you're inviting them to attend your event, they expect that you will care about their needs. Show it through social media.