Say I have an app named "Foo Bar", should the bundle identifier be com.tyilo.foobar
or com.tyilo.FooBar
?
What is the most normal and what does Apple do?
You can do any but to make life simpler and prevent common mistakes it's just easier to keep it all lower case..
But it's entirely up to you what case you use?. The only gain from using lower case is what I mentioned above