It’s not because it’s sexy and shiny and plays music and lets you watch YouTube and play great games and read blogs and twitter.

It’s not because the touch screen keyboard is pretty good and the accelerometers mean it automatically rotates the screen when you turn it over.

It’s not because the location services and built-in GPS mean it knows where you are and can do cool things with maps and friend/restaurant locators.

It’s definitely not because of the quality of the camera or the life of the battery or the slightly flaky exchange server push mail integration.

Nope, it’s more fundamental than that.

Using the iPhone is relaxing.  Seriously.  The gestures, the screen transitions, the responsiveness all combine to make a calming user experience.  No other mobile device manages to achieve this: The Blackberry is a tense fiddle of scroll wheels or mini track-ball followed by cramped two-thumb typing, all Windows Mobile devices I’ve used are sluggish and require almost pin-point accuracy with a small stick and every Nokia, Motorola or Sony Ericcson I’ve ever used has had a counter-intuitive interface a predictive text system that has made me want to smash it against the nearest solid object.

Just about the only thing that’s frustrated me about the iPhone in the last week has been level 64 on Blocked.

It’s the same with websites – great looks and expensive design are all well and good but if the behind-the-scenes team didn’t lay the foundations first you might be in trouble. 

It never fails to amaze me – why are some websites just so frustrating and difficult to use? And why, then, is website usability not higher up the agenda? If you are seriously considering a site redesign or upgrade, put aside a small but friendly sized part of the budget for User Experience testing – right through the IA, design and build phases. 

There’s nothing worse than realising the foundations weren’t properly laid and expensive post-launch fixes could have been avoided.

The process of gathering requirements and system design is always thought of as a pretty linear process.  The theory goes that as you gather more and more requirements you are better equipped to organise them and create the perfect system.  Basically the relationship between understanding and time is one-to-one.  A bit like the graph below.

Linear requirements process

If this was the case then it would make sense to spend the necessary time gaining a complete understanding of the system.  Not only is each quanta of time (let’s say a day) worth the same, if you spend enough of them you will eventually get to a state of perfect understanding which will allow you to go off and employ a team of developers to build the perfect system without any further thought.

Now everybody knows that this doesn’t actually work in practice and however much effort you spend designing a system there will always be things that for whatever reason don’t quite work in the real world.  Not everyone is quite so keen to admit that the theory is flawed so normally the blame is put on the implementation of the process:

“We really must make sure our design is more comprehensive next time.”

In reality the process of gathering requirements and system design is not linear.  There’s normally a pretty steep curve at the beginning of the process as you get an idea of the core requirements and this tends to level off the more time that is spent.  Arguably you never really get complete understanding and you can certainly never design the perfect system.

I think the curve looks a bit like this one:

Actual requirements process

So, there comes a point where it’s not really worth gathering any more requirements or spending any more effort designing the system as each day that is spent brings less and less extra knowledge.

Common sense tells you that you should stop trying to increase understanding at a point when the curve starts to level off and start building something.

When to start building

The trick is knowing how long it’s going to take to reach that point, recognising that you’ve got there and knowing what to do next…