How do you identify your most influential users?* These aren't necessarily (or usually) senior managers, they are:
Connectors - People who seem to know everybody, who always think to bring people together. They are influential because they have contacts all over the place, they think to include all the relevant stakeholders in a conversation, and can spread a message much farther than anyone else.
Mavens - People who seem to know everything, who spend an unusally large amount of time researching and teaching others. They are influential because they are trusted to make very reliable recommendations, and they put energy into spreading ideas and information.
Salespeople - Charismatic people who seem to be able to form opinions. They are influential because they can easily make people feel how they do about issues; they can take a stale idea and make it exciting, or they can throw water on an idea and stop it in its tracks.