Very cool in general, though I think it might take me a while to get used to compiler messages of the form "...maybe you meant <suggestion>?". The extra effort in checking things is certainly appreciated, it's really just the phrasing that I find odd -- personal pronouns are a little too "word-processor-ish", if that makes any sense (it just doesn't sound like something I expect to hear from a C compiler, really). I might find it less jarring if it were phrased as "...(suggestion: <suggestion>)" instead, or even just without the "you meant".
There already is a few examples of gcc giving helpful hints (although nothing like LLVM).
For example (t.cc):
template <typename C>
void test (C c) { C::iterator it = begin(); }
⋮
test(std::vector<int>());
Shows this error (with a note about what the programmer likely meant):
t.cc: In function ‘void test(C)’:
t.cc:2: error: expected `;' before ‘it’
t.cc: In function ‘void test(C) [with C = std::vector<int, std::allocator<int> >]’:
t.cc:7: instantiated from here
t.cc:2: error: dependent-name ‘C::iterator’ is parsed as a
non-type, but instantiation yields a type
t.cc:2: note: say ‘typename C::iterator’ if a type is meant
