Among the premature Google Play leaks this morning is a line about a purchase bonus, to ship alongside each Nexus 7 tablet. As a temporary incentive, Mountain View is offering customers a $25 credit to spend on Play store content, along with additional content, including a copy of Transformers: Dark of the Moon. We're just minutes away from the start of Google's I/O conference keynote, where we expect to hear full details about the tablet and bonus cash, along with a handful of other devices, such as the Nexus Q.