I haven’t used HTML5 possibilities in my web applications because of browsers’ poor support, but situation seems to become much better so I became really interested in its new cool features (even though many of them are only in a draft state today).
I already know about cool Web Sockets, WebGL and Canvas (with this stuff I can finally get rid of Flash!)
What are the new things in HTML5 that I should be aware of? (I mean new ways of web-programing not the particular tags) (the question was inspired by Google IO)
Take a look at Dive into HTML5. It explains most of the features of HTML5 in a very illustrative way. Database functionality and offline applications are two additional things you didn’t mention.