I have been working a little bit on the Android App (not as much as I would have liked, but time seems really scarce at the moment).
for anyone who would like to see some screen designs have a look at the document [https://github.com/element14/nocturne/blob/master/Design/AndysAC-Notes.doc AndysAC-Notes.doc]. This contains how I see the REST Api looking, how the screens will flow, and has my sequence diagrams and database design.
there are some png images in github [https://github.com/element14/nocturne/tree/master/Design] which show how I see the system working (these diagrams were create using the UML tool violet).
I had a look at EspressoLogic but didn't get it working, so I am currently looking into using a node.js test server for my testing.
I have been learning AllJoyn and MQTT for work, and both these technologies could be very usefull in the communication between app and server. when I get a bit more time (and a bit more experience) I will do a writeup of where we could add them in in future.
I have also been thinking about using a raspberry pi to poll the sensortag. I have a bluetooth 4 adaptor for the pi, but I don't want to start that until the android client is up and running.