So when you want to delete an app from the Home Screen, or delete a book from iBooks, when you get into "Edit Mode" there is a little itty bitty X in the upper left hand corner of the app icon/book/whatever.
Is this button part of the SDK?
And... if not (I'm pretty sure it isn't), does anybody know an Apple sample project that might contain the X image?
You could try looking in the Springboard.app. (Springboard is the home screen in iOS.) It should be located somewhere like:
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator*X.Y.Z*.sdk/System/Library/CoreServices/SpringBoard.app/
EDIT: per the comment below, the location of the images for the 4.1 simulator sdk is:
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator4.1.sdk/System/Library/CoreServices/SpringBoard.app/closebox.png /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator4.1.sdk/System/Library/CoreServices/SpringBoard.app/closebox\@2x.png