I am just now hearing about an asteroid estimated to be about 10 meters across blowing up over Indonesia on October 8. Apparently no one was injured. I have no clue how I missed this, but The Telegraph has the story. This is not an everyday occurrence, but 10 meter rocks probably do come in and explode high over the Earth's surface every few years or so. If they're rock they won't make it to the ground; instead they blow up due to the incredible force of their passage through the air (in this case, the explosive yield was about 50 kilotons of TNT). Smaller rocks will rain down, though.
If it's metal, that would be worse. It might withstand the aerodynamic pressure and hit intact. However, like I said, this is pretty rare.
The newspaper article above plays up the "What if it were just a bit bigger?" aspect, which is true enough, but what can we do? A rock or chunk of metal 30 or so meters across is dangerous, sure, but is too small to see very far out, so there's not much we can do about it. That's not exactly great news. It's possible it might get spotted a day or two in advance -- we've seen smaller ones with a day's warning -- but most likely our first warning would be the flash in the sky.
It would cost a fortune, hundreds of millions or more, to set up telescopes to scan the sky deeply and quickly enough to see all these rocks. There are some 'scopes like that in the works, but I suspect the political will to create the network needed just isn't there. It may take a few more impacts like the one over Indonesia before people start taking this seriously.