That hasn't exactly stopped them from holding detainees in Guantanamo with no charges for years, and no hope of release.
If the government gets the wrong idea about you, they may bust your door down and run in with guns drawn, then shoot you because they think you're reaching for a gun.
While I'm concerned about what Google or Facebook will do with my information, the biggest concern (and the one expressed here) is that the government will demand or snoop it from them, and act on it in one of the ways described above.
This statement is factually incorrect. The government is allowed to hold you for however long they want, without trial, as long as they call you "terrorist". www.ndaa2012.us
In the uk and the us at least this is no longer true. I they call you a terrorist (with or without proof) the normal laws don't apply. They are also collecting everything we do and storing it for as long as technically possible, quite soon that will be forever.
Government agencies are the bigger problem at the present moment in time, not corporations.