For me the exciting bit is being able to access devices from them.

E.g. I've been waiting for this for a while because you can write an app which communicates directly with an Arduino or any other serial device.

This means that a lot of special purpose desktop apps communicating with custom hardware can be written as Chrome apps and take advantage of the speed/ ease of UI development of web apps.

For one of the apps I maintain this will reduce the time it takes to make UI improvements from several days to several hours.