Nielsen's latest report sheds lights on the use of second screens. According to the Nielsen survey of connected device owners, about 70% of people report reading about other things when they watch television. About 50% of tablet users (and 35% of smartphone users) will actually look for information related to the show they are watching, and 20% of tablet users (and 13% of smartphone users) will try to find this info through social networks.
More info at Nielsen
We (i2) have just finished a project on 2nd screen with the DTG (Digital Television Group) and Technologia, for Ofcom. It's going to be published soon. If you'd like to be notified when it is published, please drop us an email via the contact page.