Brief Description: We've run into people living in a different city than the one LiveJournal thinks they should be in by their zip code. There's no way for them to give both their city and their zip code. Just let people fill in the fields themselves.
Longer description: It's a really nice feeping creaturism, and I'd gladly take it home and pet it and play with it, but when it helps, it doesn't help much, and when it hurts it's really annoying and frustrating for users. We currently tell people to not put in a zip code if they can't get their city to show up right. Strikes me as a the wrong solution.
Benefits: Fewer frustrated users. Less frustration leads to less general annoyance and malice and we hold off the Apocalypse an extra few seconds. Parents take that extra moment to smile at their children. Children take that extra moment to not slam their doors when rushing to their bedrooms to avoid their parents. And people can put in both their city and their zip codes without any problems.
Disadvantages: Every so often someone who knows what zip code s/he lives in, but is wrong about the city won't be automatically corrected. I suspect most people who mess up, mess up the other way round. But there must be someone who is going to put in the right zip code with the wrong city and say: Damn you LiveJournal for not being psychic. Oh, and whomever coded this nifty trick might be grumpy to see it removed, especially since time and effort was surely put into creating it. Maybe we should give the designer extra cookies to make up for it? Since it's still well-coded.
Implementation: Someone with clue goes in and yanks out the right pieces of code. With hope, only the right pieces of code get yanked and nothing breaks. Without luck, it turns out that all LiveJournal code depends on the code linked to zip code and LiveJournal suddenly changes into an ad for <insert least favorite company here>. *hands people some good luck*