I believe there is a difference between bool and BOOL, check out this webpage for an explanation of why:
http://iosdevelopertips.com/objective-c/of-bool-and-yes.html

Because BOOL is an unsigned char rather than a primitive type, variables of type BOOL can contain values other than YES and NO.

Consider this code:

BOOL b = 42;

if (b) {
    printf("b is not NO!\n");
}

if (b != YES) {
    printf("b is not YES!\n");
}

The output is:

b is not NO!
b is not YES!

For most people this is an unnecessary concern, but if you really want a boolean it is better to use a bool. I should add: the iOS SDK generally uses BOOL on its interface definitions, so that is an argument to stick with BOOL.