Lee McEwan on not re-inventing the wheel:

Too many agencies and brands are still adopting a not-invented-here approach rather than using the services that others have developed.

As I'm perhaps overly fond of saying, the world doesn't need yet another branded version of MySpace, iTunes, YouTube, Second Life or Flickr!  Instead, grow the potential of your site by linking into these services in every way you can. 

Ben Terrett at the Design Conspiracy provides a great example of how to build an interactive presence (for the South Bank Centre in London) by mashing up a series of existing web 2.0 services. Whilst Ben says that this was partly a matter of necessity he also notes that it benefits the user:

"Partly because of a small budget and mainly because it makes sense to use tools people are familiar with … we've used a lot of stuff like Typepad, Flickr, Feedburner and YouTube."

Ben points to one of the BBC's fifteen web principles which explains why a component model of web development is the way to go:

"Do not attempt to do everything yourselves: link to other high-quality sites instead. Your users will thank you. Use other people's content and tools to enhance your site, and vice versa."

Using existing web 2.0 services to build a site … reduces the development time and ensures that you are plugged into pre-existing social networks rather than having to create your own (as the One Million Masterpiece team learnt a little too late). It also bolsters the credibility of your site and provides reassurance to anyone wishing to contribute content that this is not just a here-today-gone-tomorrow marketing campaign but an enduring web presence.

Some of us have been doing this for a while. In evidence, I submit Voice of a City, built for Eurostar using WordPress and Flickr in the summer of '05, GooTube, a channel on YouTube we've done for Cadbury, where we're soliciting entries for the £5000 YouTube Goo-Off and Goo Earth, a game using Google Maps.