This week, I've spent App Inventor time trying to break it! The best rule of thumb I've learned teaching computer programming is you gotta know the software's weak points and exploit all of them so you know where you stand when any one or, as is typical, any sort of combination of them blow up to crash your work. And especially teaching kids, where fingers are faster and attention spans shorter so it's a given, they'll be all over the place in the software button mashing away. Which, by the way, is what lets them learn applications so quickly - they make their mistakes, lots of them, quickly, and bounce back to try different approaches. So ... that said, stuff to watch out for when using App Inventor:

**Log out of  a session after 1 hr, and log back in. I've found staying logged in to one session for an extended period leads to lags in communication between the designer/blocks and the emulator.

**Be careful using image files - unless compressed, their file size can take up your App Inventor memory store (I'm still researching to confirm these limits) ,and cause performance problems. I'd suggest copying over Scratch 1.4 sprite image files (the version that you download to your hard drive), which will typically install Scratch image files here:

C:\Program Files (x86)\Scratch\Media\Costumes

**Don't be surprised if what you see in your design view is not what you see in the emulator. For example, GIF files will play their native animation loop in the design view, but will not in the emulator, and you'll need to re-program the animation desired using the App Inventor code blocks.

** Be prepared to close your emulator and re-start/re-connect several times while working on a project. I've found that sometimes the emulator will display changes made "on the fly", other times, not. But, usually, giving the emulator some time to refresh or just closing it and reopening did the trick.

I'm still very impressed with AI! And really, these weakness give you other teachable tools, such as debugging and researching developer bulletins. Which, brings me to one last "uh oh" I found this week -- the newest version that MIT plans to use 2014 forward as their enterprise version isn't currently 100% windows compatible. Using a PC, you can access the designer and blocks (now, both web-based in the same window, so you don't have to download java to get the blocks), but you can't currently open an emulator, which is the player that shows your animation results. I checked the AI user boards, and the MIT developers are aware, but don't yet have an estimated turnaround time to release this feature for PC users (a mac version is already up and running).