I too am hoping for an improvement that will scale to a million users. But here's what I do that should scale to tens of thousands decently: I run dropboxd on

I too am hoping for an improvement that will scale to a million users. But here's what I do that should scale to tens of thousands decently: I run dropboxd on my web server. Instead of using the API, users share a folder with my app. Dropboxd gets the stream of changes, and my app polls the local filesystem for changes instead of polling across the net.