I've implemented this as a hackathon project a month ago (an iPhone serving as a broadcaster and an iPad serving as a receiver). It's an awesome technology with a lot of promise but my one BIG gripe is the imprecision of RSSI. At home, the proximity indicator was somewhat accurate. At the office the proximity indicator was not accurate at all - half the time it would be good but the other half it would show the unpredictbale/interchangeable RSSI whether the receiver was at a yelling distance or a whispering distance. (Maybe due to signal interference)?

If RSSI cannot be relied upon, it severely limits the utility of iBeacons. A "binary" result (beacon found, beacon not found) can be useful but not near as useful as a reliable distance indicator. For example, my goal for the hackathon was to see if equipment in a lab could be activated by walking around with your phone. If the phone cannot tell that I am closer to equipment A than equipment B, then there is no point and moreover, we should not be referring to this new technology as "micro locations".

Having said that, I know of a company here in Minneapolis piloting iBeacons as indoor navigation (to find your way in a mall for example). I don't know if their technology works because they've found a way to ensure more correct RSSI readings, or if they are simply relying on the assumption that stores are far enough apart.