Hashtags: the responses were split on whether events needed a specific hashtag or one that has multiple uses. A good example is #PCMA (used year-round) and #PCMA11 (used specifically for Convening Leaders). Either way, a hashtag MUST be promoted weeks, if not months, in advance and should be placed on all marketing material such as brochures, websites, e-newsletters, twitter bio, etc. For more hashtag information, check out my post on How to Create a Hashtag for Your Event.
Sponsors: some ideas for incorporating your event’s sponsors are to create twitter lists, FBML tabs on your Facebook page and to tag sponsors in your tweets & Facebook posts.
Location-based: some are just starting to incorporate location-based social networks such as Foursquare, Gowalla and Facebook Places into their event.
How are you promoting events with social media?