Lots of replies. Let me see if I can answer all the questions:
1) Does not require generating a new code for each charger expedition. If you use the anonymous sign in and delete and re-install the app you'll have to generate a new one. If you use facebook sign in your QR code should always be good even if you uninstall and re-install.
2) Why not leave your cell number? I, personally don't like leaving a unique identifier like a phone number around, way too easy for someone to find out where I live, where I work, etc..
3) How do you know when charging is done? This, to be honest was a bit of an oversight on my part. If the car has powered down while charging you don't know. I'll be changing the messaging in the app soon to say something like "There is a line for the superchargers. Check your charge level in the Tesla app or check in on your car at your convenience." I've also considered a checkin process where if you are the owner of the QR and scan it it serves as a checkin and when someone else scans it they can see how long you've been charging and determine whether to send the message.
4) Android and WinMobile - Looking at Android, a bit more complicated to do on the QR side. WinMobile, probably not enough adoption yet.
5) Useful for other chargers? Yes, but I wanted to tackle the market I understand as an owner first. I would probably do a separate app for Level 2 type chargers since the messaging would be a little different. Like "Don't unplug me yet. Download blah blah and scan the code to let me know you're waiting". A coworker of mine actually suggested I do a version for laundromats... "Don't touch my undies, scan the code and I'll be right there to unload the washer".
6) How is there a review already? It launched mid day yesterday, not sure why Apple says it was today. But if you like it, definitely review and give it 5 stars, helps people find it easier when they search.
Thanks for the feedback everyone! The app already has over 100 downloads, not too shabby for something so niche.