Google Apps script proved to be extremley useful recently when I created a small menu item that created Calendar events from a spreadsheet. Took a lunch break and 30 lines of JS to make a really efficient enterprisey interface to make large amounts of events. You can even send invites with the API!
Care to share how you've done this? We've been looking to do similar in our laboratory for the various instruments we run user samples on (HPLCs/xray/NMR). We've been using gCalendar so far, but it's not always user friendly + we have to add users to the calendar manually before they can reserve instrument / consultation time. We've started using Quartzy but it suffers from the same "must approve users first" model and we've accepted its clunkiness in the name of consolidation