Depending on what is overloading them the operators can be doing anything. If you're just using iostream I'd say it's the address of the standard output device.
cout<<(cin>>some_variable); Following my logic above this would be the standard Input device, i.e. the Keyboard.
cout<<(cout<<1024); This would be the Standard Output again with 1024 tacked onto the beginning.
Per that page, the pointer it gives you is more or less useless. It will be null if the last operation failed, or non-null if the last operation was a success.
With that in mind...
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//this
cout<<(cin>>foo);
// is the same as this:
cin >> foo;
cout << cin;
// is the same as this:
cin >> foo;
cout << (void*)cin;