Worldwide or national trending signifies a large amount of volume tweeting about a ticker..either negative or positive...eg $JRJC. so yes steve exactly social media external data. That often signals volume> = price movement. And potential useful data source to measure psychological, behavioural effects ...and how these play out on stocks.
Ideally I'd love to create some formulae that could correlate : no of tweets+ sentiment of tweet ( measured through popular adjectives) with % of movement of stock x. I believe a simple linear chart could be so useful to start with. ( there must be this data out there already? )
The data source I posted above...pschosignal or whatever it's called already has all this info on an external data source but costs a lot of money to access.
I haven't really got anywhere with this due to lack of time..but interesting signal to accompany. Another signal.
Cheers alex