While the idea is interesting, the app will have to compete with more general-purpose note-taking apps, e.g. Evernote.
For me, Evernote already provides all the individual pieces (tag by person name, record date, time and location etc.) and also allows to store pictures/audio notes, is multi platform etc. etc.
I use Evernote too for almost all my notes, but I think a very focused app can be a huge win. I did my todo's in Evernote as well, but have now switched back to OmniFocus.
I also began a "develop fast and get something out there" challenge this week. My goal is to get my app launched in 7 days. I'm documenting my progress on my blog: http://jpastika.posterous.com/. I'm not sure I'll have the app out by the 7 day mark, but I should have a functional product. I like your idea and will follow your progress!
I came up with a similar idea independently - except it was more of a social game (with foursquare-esque achievements). I envisioned a mechanism for confirmation of the rendezvous whereby both parties run the app and agree the meeting occurred and their proximity is verified. That's about as far as I got.
Edit: looks like with.me did the closest thing to this already.
Thanks a lot for posting this series Chris. As a young developer just out of college and getting started in iOS development, this is extremely insightful. I'll be following on tumblr. Good luck!
For me, Evernote already provides all the individual pieces (tag by person name, record date, time and location etc.) and also allows to store pictures/audio notes, is multi platform etc. etc.