Any company based in the EU is obliged to give users all data it holds on them if requested. Write to Facebook at Facebook Ireland Ltd, Hanover Reach, 5-7 Hanover Quay, Dublin 2, Ireland, including proof of identity and a short letter saying what information you would like.
The dashboard is the principal place to get information on all your Google services, including data from Gmail, YouTube and search histories. You can get to it at www.google.com/dashboard. Google’s Account Activity feature shows you how much you’ve used different services, and you can view Google’s personalisation of display ads at Ads Preferences.
Facebook lets you download a history of the data you’ve put on the site. Under your account settings, find and click “Download a copy of your Facebook data.” This includes lots of information that will be unsurprising — photos, wall and notes — and some bits you might not expect: I was surprised to see every Facebook event I’d ever been invited to listed. You can also request an “enhanced archive,” which gives details of your logins and logouts, IP addresses, personal details, friend requests and pokes.