The problem is that presentOpenIn... only displays a menu when there are apps installed that can open the file you're sending. iOS Simulator does not have any apps that open .txt files, so it didn't seem to be working. If you run on physical device, it works just fine.
I decided to add this for better behavior:
BOOL didPresentOpenIn = [self.openInController presentOpenInMenuFromBarButtonItem:self.buttonToPresentFrom animated:YES];
if (!didPresentOpenIn) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"No Apps Available"
message:@"You do not have any apps installed that can open text files."
delegate:nil
cancelButtonTitle:@"OK"
otherButtonTitles:nil];
[alert show];
}