Prototype
Platform
To create a code: IE 9+, Firefox 3+, Chrome 3+, Safari 3+
To view a code: iPhone with Barcode Scanners that opens in Safari. Other phones/methods coming soon. Android does not support opening .ics files.
Steps
Task 1: Make a QR code
Go to http://rscanvp.com and click "Get Started". try filling out the form (it does not save your data). Try creating a code. (It does not save your settings as you more back and forward yet). Download the code (not implemented). Inset the code into your favorite graphic design program (ie Illustrator, Publisher).
Task 2: Scan a QR code
Scan the QR code in the following poster (need link) on an iPhone. The URL goes to http://rscanvp.com/view.php  (mobile webpage); The sample ICS file is open-able in iPhone Safari (but not a web view in a different app), as well as on Windows with Outlook installed. (The Add to Google Calendar and set up email reminders is not implemented)
The scanner QR Code Scan reader works perfectly from the iPhone App Store.
Task 3: View RSVPs
Go to http://rscanvp.com/admin.php. See (fake) RSVP counts. Can edit event details and code (fake data is filled in)
To Be Completed
The creation of QR codes does not generate actual QR codes, but random binary checkerboards.
Downloading your QR code doesn't does not provide a downloaded version of a QR code.
...
The data for a QR code that is input is not saved between pages.
Code
It's best to just view it on the web at http://rscanvp.com; but here is the code. Database password removed for security. (Even though we don't use the db in this version)