RIDER SPOKE - Blast Theory

I was happy to come across work from pervasive game guru's Blast Theory this morning. Their new project which is being shown in (and around) the Barbican in London this week allows 'riders' to cycle around the area and record a private message in a personal hidden area. 

I have a few questions in my mind about this project:

What are people classifying as a private space?
What happens to the private messages after they have been recorded? 
Are they broadcast to others or does privacy extend through collation and archiving?

The reason I was interested to read about this project was 2-fold.
1) I love riding bikes! My trusty BMX has travelled with me and have allowed me to see places I would never have ventured on foot.

2) The idea of artistic-freedom i.e. allowing particpants to roam with free-will is very similar to the project I am undertaking at Almost Perfect 2007. 
The project is called 'The Journey | Ar Daith | Le Voyage'.