Two big ones that I can think of: First, Mozilla, Apple, Google and Microsoft (and don't forget Opera) are in a high-stakes tournament to produce the fastest i

Two big ones that I can think of: First, Mozilla, Apple, Google and Microsoft (and don't forget Opera) are in a high-stakes tournament to produce the fastest implementation. And three out of the four/five (CMIIR) are open source. Second, the server uses the same language as the client. This isn't a big deal yet, but I'm sure within a month or two we'll start to see some web frameworks that take advantage of this. The obvious application is validation, where constraints from the Model and Controller layers could automatically bubble up into the View layer and out to the client. But it could be more subtle. You could have a data-access layer written in JavaScript that when run on the server pulls from the database, and when run on the client pulls it over a REST interface. You could do jQuery-style DOM manipulation on the server for the initial page state, serialize it to HTML to pass to the client, and then do further manipulations on the client using the same code base. So there's a lot of code sharing across where you currently have a pretty sharp dividing line.