For many events it is possible to know who is going to be in the room before you even get there. Get the list either from the event site or one of the organizers. If they don't share the list, then ask the organizers if they can give you some idea of who to expect. Then make a list of who you'd especially like to meet. At Tech After Five events (ta5.com
) there is even an app that you can use to target contacts that would be especially useful for you.