I can where Vine can be addictive is just scrolling through the feeds that come up -- and then especially if you go into the categories that interest you (rather like trying to stop eating potato chips or Herseys' kisses). Six seconds is a perfect length of time to take a quick video of something that happens in an instant, but for library use, you would have to plan out what you are going to shoot very carefully in order for every bit of the six seconds to count. I don't know if I would ever use it for library use, but I can already think of several video shorts I have taken that were not worth the trouble to upload to YouTube, but would work really well in Vine.
I tried out both Socialcam and Magisto for creating videos. Sociialcam was pretty easy to use, recorded voice easily and had a nice variety of types of title effects. Using the filters can take a while to figure what works best -- I ended up with a slightly muddy looking product, but that could have been because of what I was filming and the lighting available. Filming with a iPad can be slightly cumbersome, especially if you are holding it with one hand, while trying to focus or enlarge with the other (shaky results ensue). It will take a bit more playing around to fully appreciate its capabilities.
The first thing I liked about Magisto is that you can make a video out of still photographs -- rather like putting together a slideshow with music and transitions. You can shoot a video, and just use that video or add photographs as well. There are a variety of themes you can choose from, but you are left guessing as to how they will work in your movie until you get the "draft" and play it through. The music options change with the themes, but you always have the option of adding your own music -- and I believe you can set how loud or soft the music plays in the video. Aside from the title, you cannot add any other text to the video unless it was created as a graphic image. It will take a bit more playing with to discover if you have any control over the order of the pictures/videos in the movie. The draft stays available for about 30 days and then gets discarded. Until you "keep it" you can "tweak it" and change every aspect, from what photos/videos are in the movie, to the themes and music. And it does take a bit to find, you can delete (same for Socialcam -- I had to go to "help" in order to figure out how to delete my test video). Magisto's movies are not immediately available -- it does take a few minutes to "cook".
I can see both of these apps useful for creating relatively on the fly types of videos on a mobile device. On desk-tops/laptops similar there are things like Jing, which has been used by reference staff to explain how to use a reference source.