I don't know anything about C-4 explosive. But from what I have been reading on the FR threads, he had enough C-4 in his shoe to blow a hole into the center fuel tank over which he was sitting. You don't need much C-4 when you have several hundred gallons of jet fuel under you.
Good point! Maybe the days of online "pick your seat assignment" should be over. If not, at least the security should carefully profile seat assignments in "critical areas".
From the pics of this dude I wouldn't have let him within 3 miles of an airliner. No bags checked or carry-ons on a transatlantic flight? "Well he had a passport ..." - from Holland where they recently had thousands of blank passports stolen ... Looks like they hammered his left eye pretty good. Way to go guys!