I don’t really know enough about Prism to comment all that much on it.
I did notice that the number of reports that GCHQ is alleged to have compiled from ‘harvested’ data in the past year is 197. As I understand it, the programme will monitor billions of pieces of data and will only highlight stuff containing certain word patterns which indicate use of coded language common to terrorist groups.
Of course that’s fine if the parameters are clearly defined but the concern has to be that once established, there will be a temptation for authorities to use and abuse the monitoring of emails and postings on social media.
I think the days of the authorities being interested in stuff like “Just had fish and chips – there goes my diet lol!” are still some way off.