Idea [#2] - Event Specific Social Experience
I was thinking that it would be cool if you could use your mobile to make group based decisions at a concert or bar. Say your at a concert and at the front of the building is a QR Code. The code takes you to a mobile site that has a list of all the songs the band may perform, say 1.5 times the number that will actually get played. Then on the site you and everyone else will move your favorites to the front of the list, or maybe just pick 5 songs. Before the band gets on stage a "magic process" runs and produces the playlist based on the whims of the crowd. I'm not a musician so i'm not sure if playlist chioces are written in stone for some reason, or if they are mutable.
Another nifty thing would be to have something on your mobile where you define your mood and it's locally queryable. So then when you walk into a Starbucks, the store checks your mood and matches it up with everyone elses. So if everyone in starbucks is depressed then something slow and mellow plays on the stereo and if everyones happy something a little more upbeat is played.