You have to pick:

We'd have ten years to dig whale-bunkers and reinforce the roofs of our bigger, tougher buildings to survive the whale rain. Bad, but not unsurvivable. And we'll have a lot of whale meat to subsist on while waiting for the ecology to recover (we'll have to stockpile preservatives and the equipment for making whale jerky, or mine the vast deposit of frozen whale meat that would cover the Antarctic).

I was discussing this with some friends and one argued that the kinetic energy of that many whales hitting the earth at terminal velocity would be worse than a meteorite. It would cause tectonic shifts, volcanic eruptions (including the Yellowstone supervolcano) and a huge dust cloud that would create an unsurvivable nuclear winter.

Whales rule!! Do they breed like monkeys? More the better, I say

That seems like it would be absolutely catastrophic. There's the case of matter displacement, since everything would take up so much more space, but also the factors of environment (there'd be millions, if not billions of land-locked whales, unable to move, waiting to suffer and die), not to mention the food chain would be virtually nonexistent, causing most life on earth to starve.