A recent Guardian (UK: http://www.guardian.co.uk/technology/2013/jan/23/google-transparency-report-government-data-privacy?INTCMP=SRCH) article discusses a recent Google transparency report in which google discloses the numbers of government requests for data. Of the 8438 requests (from 6/12-12/12), 68% were made through ECPA supoenas (which don’t require a judge’s approval), 22% were made through ECPA search warrants (which do), and the final 10% were through ECPA by judges. The article states that google complied with 90% of these.
Google’s transparency report: http://www.google.com/transparencyreport/userdatarequests/
For one discussion of the challenges of ECPA, see Pell, Stephanie K. and Soghoian, Christopher, Can You See Me Now?: Toward Reasonable Standards for Law Enforcement Access to Location Data that Congress Could Enact (April 21, 2012). Berkeley Technology Law Journal, Vol. 27, p. 117, 2012. http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1845644
Update: Twitter is also choosing to self-disclose its government requests, according to PCMAG (http://www.pcmag.com/article2/0,2817,2414784,00.asp). See: https://transparency.twitter.com/. Perhaps this is the beginning of a new movement is self-regulation and disclosure. Now if only firms would choose to disclose, for instance, the number of times they collected, mined, and shared our data.