poli sci guy dan smith at the university of florida has written/co-written quite a bit on above, this website includes a number of articles on the topic (and some other matters as well): http://www.clas.ufl.edu/users/dasmith/pubs.htm
you might check out the initiative and referendum institute: http://www.iandrinstitute.org/
and the ballot initiative strategy center: http://www.ballot.org/
and if you want to make/take the time and put forth the effort, here's some books:
Dan Smith & Caroline Tolbert, Educated by Initiative: The Effects of Direct Democracy on Citizens and Political Organizations in the American States
Elisabeth Gerber, The Populist Paradox: Interest Group Influence and the Promise of Direct Democracy
Richard Ellis, Democratic Delusions: The Initiative Process in America
Shaun Bowler, Caroline Tolbert, & Todd Donovan (eds.), Citizens As Legislators: Direct Democracy in the United States
above is just a start, will be happy to provide more sources but you're probably already tired by now... michael hoover