On it's own, my Verizon Droid Razr (recently with ICS), went into debug mode. How do I get it out of debug mode?
Do you have "{} Developer options" under Settings menu? If yes, go to Settings->Developer Options and uncheck the boxes under "Input", "Drawing" "Monitoring" sections.

I presume these should be not available with standard ROMs (i.e. produced by carrier/that come with phone).  In that sense, I am bit surprised on why you have it, unless you have CM's or other similar ROM.