Interesting concept. I started in the SF bay area in the US, and did not see anything. Then I zoomed out all the way, and Australia lit up with notes :-)

Do you plan to add a timeline? It can be interesting to see opinions about a place over a time period.

powered by mongoDB + node.js under the hood.

I actually wrote my own KeyVal over Postgres in js. It worked fairly well, but got better perf with MongoDB which I found quite sane and easy to use.