It is crucial that technology be tied to a real objective; otherwise it is simply the use of technology for the sake of just having it. That's wasteful. It is especially so when there are actually so many innovative and interesting things that can be accomplished with what technology has to offer now.
Students should always be held accountable for what they do; utilizing technology is no different. They need to realize that just because they are being handed an iPad and told to use an app, that it is not license to play around mindlessly. It would be even worse if they were to handle the items carelessly and cause some harm to come to it--the district has worked too hard to get these things into our hands to allow them to simply be broken.
I think that Bubble Us is an excellent tool for pre-writing. There are many students I can think of who would benefit from the structure of it more than being given simply pen and paper. Lexipedia could be especially helpful for ELL's to build lists of unfamiliar words while reading. These lists can then be connected back to vocabulary that they do know, and they can continue to build their skills.
As for apps, I like Poetry Creator. Many students dislike poetry and find it difficult to create, but this app would streamline the process and hopefully help them to see how phrases come together as poetry. I've mentioned Skype in a previous post, but I think it could really open the door to interesting topics with interesting people.
Since I don't have many iPads, I think they could be used for group review using customized flashcard apps. We could also probably do a round robin peer edit with google docs and different colored text in groups.