I like this post from Dan, where he nails two screaming goblins to the plank of truth with a single swipe of his brain hammer:

1. Why is threading not a standard part of the UI? The iPhone (which I'm using at the moment - expect a monster post some time soon) just does this, without any fuss... and it's beautiful. We've been so stuck in the "flat inbox" view of SMS for years that we consider it normal;
2. On his point re upgrades to handsets: he's spot on, and I think this is one of the things which has slowed down the rate of progress of the mobile internet (when compared to the fixed internet);

I've heard a justification for the latter, told to me in confidence by someone from a handset vendor: that software and infrastructure to OTA updates of firmware exists now, but that it's awaiting a product manager brave enough to roll it out into a handset for which they take responsibility... the problem here being bonus structures. If a product manager launches a device that generates loads of recalls (i.e. has high-risk features), it's possible that they'll take a financial hit personally.

I'm not sure how true this is (though my source was in a good position to know ;)), but it's a lovely example of optimising behaviour around numbers if so.