it's true that there is nothing to stop someone from running a brute force attack on a one way hash. However, the reason that people are encouraged to occansionally use non-alphanumeric characters in passwords is simply to slow the cracker down. Using upper and lower case letters increases the number of possibilities from 26 to 52, using numbers increases it 62, using non-alphanumerics increases it again. All highly worthwhile practices. This is also the reason for having as many characters as possible in the input string and stay away from real words, both of these techniques slow down a cracker.