Here's one more thing for the list: you need an API. And here are the top five reasons why:
1. It's Good BizDev 2.0
Having an API is, as Caterina Fake calls it, BizDev 2.0. In other words, in a web-oriented world, it's the way business development is done. APIs facilitate business-to-business relations by opening data and systems to business partners, either freely or via a commercial license. The integration with other services provided by APIs makes doing business, in Fake's words, "much much better."
2. It Builds a Strong Developer Ecosystem
An API allows you to interact with developers outside your team, adding expertise and innovation to your product. Releasing an API also adds to the proverbial tool in a developer's toolbox.
3. An API Facilitates Data Accessibility
Having an API makes new queries easier, making information discovery easier for you and for others.
4. Investors Are Going to Want One
"Not all of our companies, by the way, have launch read/write API's, and we're constantly hounding them to do that," said Wilson, "but the important thing about programmability is that when people can add value to your application, they are in effect adding energy to your application, bringing more users to your application, and also bringing more data and more richness to your applications."
5. APIs Make Mashups
...And mashups are awesome. Facilitated by APIs, mashups bring together information and applications in unique ways, expanding the reach of your data and product. A mashup that combines data from Google Maps plus YouTube plus World Cup, for example. A tool to automatically add all Nicholas Cage movies to your Netflix queue. Powerful stuff.
As Fred Wilson notes, you don't necessarily need to have an API ready at launch. But it should be on the short list of things your startup needs to implement.