My colleague Victor just wrote a great post.
From his post:

What is the service this site is providing me – or to put it another way – what’s in it for me (other than a way to waste 10 minutes of my day)?

It’s important to answer that question before your client does.
We all have to make a living, no one likes to turn down interesting work and I wouldn’t be where I am today if I didn’t know Flash and HTML….
…but – that doesn’t mean we shouldn’t question the type of interactive work we’re producing.
Why Does This Site Exist?