In this new post Joseph Scott takes a look at hashing in PHP, specifically around md5 hashes, and a better alternative (that's also more secure.

The majority of the Coding Horror: Speed Hashing post talks about speed based on MD5. [...] If you are still using MD5 to hash passwords (or worse, aren't hashing passwords at all) then please stop and go use bcrypt. For those using PHP phpass is a great option.

He talks about the crypt method, how its encryption method and "cost" value effects the speed and how difficult it would be to generate all possible hashes for a password (hint: crypt with a cost of 13 is worlds better than md5).