The mere fact that you have to use smart pointerS is enough of a drawback; not only do you need to start decorating various types explicitly, but you must choose which smart pointer types are appropriate, and avoid issues of circular references (in the case of refcounting) and persistence of references (in the case of scope-guarded objects tied to a stack frame); worry about logical ownership hand-off from one smart pointer container to another, etc.
The real power of GC, though, is freedom to use idioms that are simply impractical, or especially, not exception safe, in its absence (see my comment earlier).
The real power of GC, though, is freedom to use idioms that are simply impractical, or especially, not exception safe, in its absence (see my comment earlier).