There is a lot of hype going around at the moment related to the wonderful functionality that websites will be able to offer once browsers implement the so-called "HTML5" features.
Some features should enable graphical capabilities without requiring a plugin (bye bye Flash), others are targetted at mobile devices - such as enabling the capture of an image from a camera.
The one that has been most relevant to my current project is Web Sockets.
In my opinion the key to Web Sockets living up to their full potential is that http servers must be able to support the model of keeping connections open.
At the time of writing, Apache httpd does not support this as it is architected for synchronous processing of requests and sending of responses.