There is a proposal pending for C++1z (the next standard after C++1y will be standardized into -hopefully- C++14) that aims to remove trigraphs from the Standard. They did a case study on an otherwise undisclosed large codebase:
Case study
The uses of trigraph-like constructs in one large codebase were
examined. We discovered:
923 instances of an escaped ? in a string literal to avoid trigraph
replacement: string pattern() const { return "foo-????\?-of-?????"; }
4 instances of trigraphs being used deliberately in test code: two in
the test suite for a compiler, the other two in a test suite for
boost's preprocessor library.
0 instances of trigraphs being
deliberately used in production code. Trigraphs continue to pose a
burden on users of C++.
The proposal notes (bold emphasis from the original proposal):
If trigraphs are removed from the language entirely, an
implementation that wishes to support them can continue to do so: its
implementation-defined mapping from physical source file characters to
the basic source character set can include trigraph translation (and
can even avoid doing so within raw string literals). We do not need
trigraphs in the standard for backwards compatibility.
