Budget versus actual revenues and expenses
Value of sponsorship revenues both cash and in-kind
Registration numbers at pre-determined milestone dates
Final registration numbers
Post-event survey results about speakers and content
Test scores of participants
Number and quality of leatuds generated (if "quality" is clearly defined)
Staff satisfaction survey scores
Waste diversion rate Percentage of locallorganic food served
Participation rates in a community service project
Meeting milestone dates in the critical path
Social media statistics (for example, number of tweets, use of the event hashtag)
Web site visits
Response to e-mail and mailing campaigns
Response rates to surveys?