Jumping in here, the problem is that having to mix GC code, which automatically releases memory in a non-deterministic way, and normal RAII destructor code, which releases all resources in a deterministic way, creates two different syntaxes in a C++ program. This would currently require the programmer to "know" which type of destruction belongs with which object.
Unless the same external syntax can automatically be used on all objects, where the classes of those objects which need deterministic destruction automatically use RAII destruction whereas the classes of those objects which only need non-deterministic destruction use GC, I do not think C++ programmers will ever be enthusiastic about using a garbage collector. At least I know that I won't and will stick with shared_ptr with the occasional scoped_ptr/weak_ptr until a way to syntactically unite RAII and GC is accomplished.
GC has successfully masked the fact, in langages/environments like Python, Ruby, Java, .Net, that it is a very poor system for dealing with any resource other than memory.
The way of releasing resources may be dependent on the type of object. If you use my GC (http://sourceforge.net/projects/sgcl), you can write: class Foo {}; class Bar : public Limited {}; gc<Foo> foo = gcnew Foo; gc<Bar> bar = gcnew Bar; Bar-class destructor will be called in a deterministic way.