I just spent the last month writing TheAudioDB with the intention of using all this newfangled web technology. Being an oldschool php programmer its quite a jump and I ended up using a lot of old technology in the end.
Would be very interested how you got Jeditable working and all the Jquery stuff. I spent hours trying to work that one out!
I found the Jquery slowed the site load times down a bit and didn't work on all browsers. But its certainly the future, I'd love to have database popup modal boxes that were editable.
Also well worth checking out EZSQL if your using php/mysql still. It simplified the development so much.
As for the API, go JSON, its so much quicker to produce and also has a nice size reduction due to the small tags.