For anyone that's developed an extension or other integration with CiviCRM, you know how important a good api is. CiviCRM's api version 3 is incredibly useful - it's mature, stable, tested, robust, and even has a handy gui explorer that writes code for you!
Great as it is, api v3 is now 5 years old, and while it may well last another 5 years before being retired, it's time to think about the future. Over the last 5 years it's managed to build up a fair amount of cruft and oddities, which we keep around for the sake of backward-compatability. Bumping up to version 4 represents a chance to start with a clean slate, lose the cruft, and embrace new technologies and techniques.
There's much to discuss and lots of exciting possibilities. Come join the conversation!