Had these majorities swung to Labour instead then the Conservatives would have had only 324 seats out of 650, which is technically a minority. And for that to happen, what's needed is for half of those forming the majority to switch from Conservative to Labour. For example, the majority of 27 in Gower would have been wiped out if just 14 people who voted blue had voted red instead. Not voting one way brings the majority down to 13, and then voting the other way creates a Labour majority of 1.
Adding these seven figures gives a total of 901. OK, so that's one out from my rounded figure, but you get the idea. 901 voters choosing to back Miliband rather than Cameron would have cut Tory support sufficiently to create a minority Conservative government. And yes, that's only technically, because Sinn Féin never turn up at Westminster so the winning post is effectively 323, and yes, even with 320-ish MPs the Conservatives could have ruled from a position of effective control.
But the fact remains that there are fewer than 1000 people out there on whose choice the outcome of this election hinged. If you changed your mind in Gower, Croydon Central or Bury North, one of those people could be you. Thank goodness nobody knew who you were before the polls opened, otherwise you'd never have been left alone. Electoral reform, anyone? Or does this random selection of a handful of VIP citizens actually work rather well?