I like all these answers so far - extending to mobile devices
I saw a documentary the other day where a service stored 1000's and 1000's of pictures of a city in it's server.
People take a photo of a landmark with their mobile and send it to this server, which matches the photo with one in it's store and then sends the recipient information (eg. history) about that landmark.
I suppose web 2.0 is alot about the social web, but it's also been about the platform and technologies that enable mashups, re-syndication, etc...
Is web 3.0 going to be the semantic web, that's probably web 8.0 or web never.
A feature of Web 3.0 could be services like Dapper and Ning which goes beyond Read/Write, it's more Create/Read/Write.
With Ning non-techies can create applications, with Dapper you can mashup them up