Sustainable Web Development must go beyond money and effort and enters into the realm of public good. Public good means that consumption by one individual does not reduce the good available for consumption by others. A pure example of a public good is air - you breathing it doesn't stop me from breathing it (water was once considered a public good, but alas, times change). Creative works are often referred to as Public Good.
In economy, this topic is highly theoretical, however the Internet starts to offer new examples that are real. This is not to say that the Internet itself is a public good, but accessibility of it is (or should be).
Open Source Development and the buzz word Web 2.0 has marked a clear shift towards Internetworking as a Public Good. Social Networking, Media Sharing, Syndication, Blogs, Wiki's, etc all aim towards sharing and playing well together. Creating software that can mashup with other software is becoming more and more prevalent.
Actually using the web for more than reference and email has drastically changed in the last few years. No longer do you need to be technically savvy (or have a friend that is) to publish, communicate or assert yourself through this medium.
But what is the endgame of Open Source and the Web 2.0 trend, fad, crazy ... whatever you wanna call it? Is it sustainable or is it a burst of energy that is propelling the Internet in order for the private sector to take it over to do business through it?
Big business is scrabbling to know what to do with social networking and free-wheeling content sharing. What will prevail or more pointedly, what should prevail?