Cool concept. Do you plan to ingest data from anywhere other than manual user input?
Other than that I'm planning to reward people based on their predictions of what could become a trend. The earlier they are and the bigger the trend the more points they get. Then votes from these people would weigh more in the algorithm which could potentially increase the accuracy and also incentivise people to input data :)
Perhaps it has changed since I used it last, but Twitter's API will give you a very limited amount of data unless you're prepared to fork over the big bucks.