I am really unfamiliar with iOS but it blows my mind that this doesn't exist already. It seems like a no-brainer for a feature, especially since Apple basically invented the modern mobile app store.
I'm wary of this. Would like it as an option, but I don't necessarily want my app to change between uses, especially if it's something I need to use quickly. Loading up something with a changed UI, or data changes that need to happen, or whatever, when I wasn't expecting it.... won't make me a happy camper. A notification and ability to trigger the update from in the app would be nice, and having the option of 'auto update' would be nice too. I just don't necessarily want it to be the default with no option to opt out.
I think that as developers, we'll need to be very careful to update things incrementally to not jar users. But overall, it should be a win in that just like with a website, the user is always using the latest code. No need to maintain several old versions of web service APIs, which should have a good effect on reducing bugs.
