I'm a bit surprised that no one has posted here recently; there has been a lot of excitement about the field testing in the US.
In case you guys haven't heard, testing has been released to many people on America's West Coast, specifically those in Southern California (areas such as OC and LA especially). A friend of mine was admitted as a participant and just downloaded Pokemon Go today. Here's some interesting stuff I found:
The mechanics, from what I saw on their phone, can show local gyms and areas where items can be picked up for free (iirc). Several of these appeared in a 1-mile radius from where we were, but I don't know how far this radius extends. Pokemon can be found in many places, so it's not like they only appear in set, meaningful locations from what I can tell.
We found a wild Eevee, but we were in class and couldn't go catch it, so idk if it's still there or if Pokemon despawn over time. Not sure how rare that is either. I don't know what effects occur when you approach a Pokemon, but given that what we saw with other stuff was accurate, I expect that it should look the way it was shown in the trailers.
The app uses GPS and seems to be tough on the phone's battery, but I don't know if this is a problem for others.
Everyone gets a starter, of course, which is can be one of the Kanto starters. I think it's possible to just start with a random wild Pokemon and use that instead (random meaning you go outside, find some ekans or something, and use that, not like they give you something random and it ends up being a shiny Rayquaza).
Nicknaming exists, and you doesn't need any money or anything like that; it can be done for free at any time iirc. We successfully named the starter Bulbasaur "Bulbab*tch" so I guess swears are allowed. You can change the names as many times as you want too, I believe.
Basically, the hype seems to deliver, but the content is still being explored. Some of this may be common knowledge but w/e, thought you all might be interested.