My biggest concerns with the introduction of technology into the classroom are that first, we don't really have any killer-app that justifies the expense,
Not entirely correct: As a math teacher I have found that Desmos (.com or app) is a remarkably good graphing calculator for mid-range algebra 2 students. When the alternative is an $80-120 graphing calculator, it has its appeal. Khanacademy.org has extreme value, when used for extra practice, and digital copies of texts are more prevalent, though current methods of DRM make them often more costly over time than the physical version, if not more up-to-date.
It's extremely easy to get off-task when you have the bulk of the Internet at your disposal, even if there's content filtering. General purpose computers give students almost unlimited choices in what to do, and only one of those choices is the intended one.
This is absolutely true, and the main reason that while I recognize the potential value of cell phones, I generally see greater problems in the classroom with their use.
One thing that hasn't been alluded to yet that I think is VITAL: my students exhibit high levels of technology dependence. Their every spare moment automatically drags them to their device. This is leading to a growing situation where they will entirely ignore a class-wide announcement unless they have been called to attention BY NAME. It's reaching greater levels of absurd every year.