And I'll add a couple thoughts about side-curtain airbags (applicable also, but maybe to a lesser degree to side-seat bags).
I'd probably be dead today were it not for the side-curtains in my late 2002 Camry. That car was an I-4, 5-spd manual stripper, but it had the curtains. I picked it sort of on a whim -- there was an identical one, minus curtains, for about $500 less. To this day, I'm really not sure what made me pick it -- I was only barely aware of the existence of side-curtains back then. Spooky...
In early 2003, I got T-boned hard by a full-size SUV whose driver said he was doing about 40 mph before impact. Last thing I saw was the grille, seemingly about a foot from my face, and coming fast.
And then the curtains deployed. Wow. They come out faster and harder than frontal bags do, because they have much less time in which to perform their magic. They hit you hard, and it hurts. But it sure beats having your brain sucked through a Tahoe's radiator.
Anyway, as you all can imagine, I've had plenty of time to ponder this, and I'm left with a couple lasting conclusions. First, I will never, ever, ever own another car with no side-curtains. Even in a large, heavy car, the point of impact for a side hit is less than a foot from your outboard elbow. Unlike a frontal impact, there's just not enough metal and space to make a real difference when the hit comes from the side. I'd rather be in a Corolla or Cobalt with side bags, than an Impala or Accord without them.
Second, I'm a little surprised, looking back in time, that frontal bags came so long before side bags. Frontal bags are great, and offer critically important protection, but side bags make a much bigger difference, IMO, compared to cars without them. Heavy flanking collisions, that used to mean certain death for those on the impacted side are now routinely survivable. Witness my own continued existence... Think about it -- in a frontal crash, you've got all that car out in front, AND the bag to protect you. From the side, all you have is a few inches of door (beam or not) and a piece of glass.
p.s./btw, I'm now probably the most paranoid cross-street checker on the planet.