I've found a couple of instances where the game is prevented from loading, and one where the game froze the iPhone.
I'm running on an 8Gb iPhone (not 3G), and I'm currently Cat 7 Lvl 1.
When in the smith, I selcted a blueprint to build, then before starting the build, I put the phone to sleep using the power button. When I went back to teh phone and unlocked it, it came back to the smae screen, so I selected the build option. Having done that, the phone froze. I had to power down the phone and restart it to do anything.
Since that, if I suspend the game at any point, except from the inventory screen, the game will refuse to load until I turn the phone off and back on.
In the inventory screen, despite having completed several blueprints, there is no way to equip the items created. I think this is a known issue, but I'll note it anyway.
I've had similar experiences, and although I have an iPod Touch, sometimes putting it to sleep, then waking it will crash the game and take you back to the main screen, and then AF becomes impossible to start without a reboot. This is noted and will probably be one of the stability issues that'll be fixed.
The lack of the function to equip items is also noted and will be fixed in future updates.