There ARE legitimate resources and reasons for "password cracking", such as lost passwords, maliciously changed passwords etc., but I've always reckoned it's best avoided in public discussion, as elite tools may fall into the hands of fools - (the real undesireables, of course, already have better tools than that).
If it's good enough for TechTV....
http://www.techtv.com/screensavers/answerstips/story/0,24330,3504258,00.html
These methods will NOT allow you to remotely hack a system that is adequately protected, though it's no secret that if any hacker is able to walk away with (or download) a Unix password file, the first thing they will do is to hit it with "John the Ripper" - admins can use the same tool to look for weak passwords.