Personally I love mashups the idea of taking two or more datasources and putting them together to give a brand new application seems such a good idea. I've just come across this application which takes the whole idea of mashups to another level.
The SekaiCamera takes information from your iphones camera and using your location feeds you information about the area you're looking at as tags, so for example say you were on a high street you could look at your phones screen and it would tag each shop with information about products, prices, etc. Or highlight events or online photographes taken in that location from say Flickr.
It would be amazing to take this idea one step further and have it as a HUD display on your sunglasses but I guess I'm getting into Minority Report territory here. I wonder how long it will be before marketeers realise the potential of this application to drive people to their store with offers etc.