A global social network
Like most people I'm sure I find myself coming up with dozens of ideas for different websites. Useful little things that would really help me and, hopefully, other people. To date I've not developed the expertes to fully impliment and deply any of these, but I often find myself nether the less going through the whole design process. Practice makes perfect, right?
For almost every idea I find myself needing to impliment some social network or another. People need to be able to find friends, manage their status with them, apply some attributes to them, send them messages and interact with them in different ways. And every time I find myself thinking "Who is going to manage a social network just to send them a recipe/file/picture/phone number/whatever?". If it was a comprehensive, well built service like flickr, then yes. But for my little start up project? No.
And so every time I find myself wishing that there was a popular social network system with a decent API that lets me as a developer attribute the data I need and the user have the power of what information goes where, and who they are friends with and how.
Some websites allow you to enter your username and password for an IM account and it will find which of your contact list are already signed up to the service. Which is great for large websites, but not so much for smaller websites whom no-one trusts.
Some popular social networking sites provide an API to interface with their social networking system. Which is great, except I don't know of any that is used by any popular sites. While it is still a bonus that people who happen to use that site as they don't have to add their friends, everyone else does. I know a lot of people who don't have a myspace/facebook/flickr/lj. Why should I limit myself to only streamlining a small proportion?
Maybe I could use all the API's to allow the vast majority of users a streamlined experience. Which is currently the best solution I can think of. But this means a lot of work trying to find a way to integrate all these services.
Even then you are limited in what you can do. I have to impliment a large number of duplicate features outside of these services, such as PMing or any form of management with these services.
What would be really helpful is if someone could come along and design a service that allowed people to manage their social networks, as well as allowing developers to create their own services that interact securely with the social networks, sharing data and allowing the user to cut down on the amount of work they have to do managing their friends. Then they need to convince some big name players such as LJ, myspace and facebook to sign up.
A man can dream.

Comments
While reading your article I was thinking:
"What's needed is a hosted service that creates its OWN api based on whatever (sometimes horrendous) HTML parsing is necessary, and hides all this from developers and presents them with a clean, consistent API for whatever service they want to link to". Then I got to your last paragraph that essentially alludes to the same thing.
I'm director of a commercial hosted website management service (avoiding the constricting CMS acronym, plus my clients wont relate to it, plus we will do more than a CMS)
Our service SiteSpark.com.au will integrate various APIs to allow our customers to blog/update popular social sites from their sitespark account; livejournal.com, blogger.com, youtube.com, flickr.com and myspace.com to start with. Of these only MySpace presents a significant hurdle (they dont have an API, and likely never will) but there IS a way.
We're strong proponents of Open Source, and have planned to offer components of our system as Open Source and also develop related free services. We also have 1 service thats in development to be offered as an independent entirely free service. This 'universal api' concept would be very cool as a standalone hosted service. Contact me if you want to chat about it.
Cheers, Morgan