I was working on a test game using Unity3D v4.5 when I bumped into a few quirks here are some quick notes so you don't need to scratch your head like I did.
How Do I Get Rid Of 'Developement Build' Text?
One of the strangest thing is the word developement text that's constantly hovering on the lower right corner of your game EVEN if you set Unity to NOT build a developement build, even if you compiled your Windows Phone app in RELEASE mode. The fix was simple enough, you set the build configuration to MASTER mode.
I did a quick scan of the build settings but I couldn't find any difference between Release and Master but it works interestingly enough.
Why Is The Windows 8.1 Visual Studio Project Meant For ARM Processors?
Trying to run the Windows 8.1 (and possibly the Windows 8.0 one as well) Store project built by Unity will give you this error
Error : DEP0700 : Registration of the app failed. Windows cannot install package SappyUnity because the package requires architecture ARM, but this computer has architecture x64. (0x80073cf3)
For those of you unfamiliar with the ARM term, that's the processor used in devices like Windows Phone, iOS, Android and also Windows RT based devices. The processor you are running Visual Studio and Windows on is x86 so you'll need to do a quick switch so you can run and debug the app on your local machine.
Select Build-> Configuration Manager
Then in the configuration screen that appears, select x86 from the drop down on the top right.
Note that you also have to change the configuration to Master to remove the "Development Build" text from the screen. And also when you're building for the Windows Store you need to build BOTH an x86 and an ARM version so that you can have the widest potential audience coverage.
Lock Your Windows 8.1 App Orientation
By default the generator Windows Store app by Unity doesn't lock your app to a preferred orientation, so do remember to open up your Package.appxmanifest file and lock your app to landscape or portrait orientation depending on your requirements.
SAVE YOUR SCENE FILE!!!!
It's soooooo easy to make games in Unity, you drag some objects onto the scene, you attach some behaviours, press the RUN button a few times to debug your game. And all is good! Then something causes Unity to crash, you restart Unity and you find yourself staring at a BLANK SCENE!!! But all your assets like scripts, prefabs, etc. etc. are all ok.
This is because unlike working in a compiled system like Visual Studio, work files such as opened scene files aren't saved in Unity when you hit the RUN button.
So do remember to SAVE OFTEN!!! Lest you lose ALL of your work because of some accident!