If you mean after generating a hash you can compare it to your list of hashes then that saves time for cracking every password, but it's slower than cracking one password. Assuming you wanted to crack every Facebook password this way, that's not going to fit into cache and a binary search into RAM is actually rather slow. Yea, you could have more computers doing just this, but it's much slower than computing the hash in the first place.
You wouldn't need to do a binary search. The values are already MD5 hashes. You could do a hash table lookup in just a few CPU cycles since computing the hash is free.
Good point, though at a minimum you need to touch main memory twice which is 200+ clock cycles. And in practice that O(1) has an much worse constant factor.
