Also, a very easy security feature I hadn't though of until was mentioned by a 'genius' at the Apple Store...the numbers don't all have to be different. Obviously you don't want something like 8 of the same, but if you double or triple up a couple times, it exponentially expands the pool of probabilities that any hacking must deal with.
Why would you even think that the numbers have to be different? It would make it a lot easier if a 6 digit passcode only contained different numbers - if the one who attemtps to crack it knew that. Luckily, it's probably not something you assume, when cracking a passwort. Take the passphrase "whywouldyoueventhinkthat"... you wouldn't change that because some letters are used more than once, would you. and, because of it's length it's probably a lot safer - and easier tonremember - than something like "G5!hebifk5".