The SitePoint PHP blog has a new post today about the challenges of password hashing and some of the common risks that can come with it. It's a continuation of a previous article about the actual techniques for hashing in PHP.
The fact that the output of a hash function cannot be reverted back to the input using an efficient algorithm does not mean that it cannot be cracked. Databases containing hashes of common words and short strings are usually within our reach with a simple google search. Also, common strings can be easily and quickly brute-forced or cracked with a dictionary attack.
He points to a video demonstrating a method for getting the password data and why just salted hashes aren't a secure method for storing this information. He mentions a "randomness issue" (and PHP's rand function). Instead, he shows an example with openssl_random_pseudo_bytes o pull a chunk of randomized data. He then talks some about password stretching using the PBKDF2 handling in PHP. Finally, he goes past the hashing and gets into encryption, mentioning "password tweaking" as an alternative to generating a single key for every user.