an interersting feature of large systems run by large organisations is that, somewhere, sometime, someone is going to turn out to be bad - an argument used by the security research group in cambridge against many systems that share too much data (e.g. children's data base in UK, the HMRC fiasco, the NHS patient record spine).
So to date, we havnt seen any massive abuse of google (or yahoo or hotmail) huge repository of personal data evidenced by large scale misbehaviour - why is this? the penalties for someone accepting bribes, or being blackmailed would be no higher than those for someone working for a UK government agency that abuses their access to private data.
I don't think the procedures employed by the large scale search engine/mail/socal net systems are inherently immune from misuse of power by an insider especially more than the UK governemtn's "transformational" systems - by the way, what a great phrase
transformational government is ! given what most of the attempts to federate government databases have achieved, there has surely been a transformation
from Blair to Brown....but it has largely been one of rapidly increasing entropy, as the pathetic IT-consultant-ignorati that they contract to for these giant projects screw up again and again...oh well. maybe thats it - maybe most people in yahoo and google are paid well and enjoy doing a good job too much to do a bad thing:)