> If you consider it a GC then it's the fastest GC. It's also deterministic and does not pause.

No, it's not, not unless you use a lot of cleverness. "We find that an existing modern implementation of reference counting has an average 30% overhead compared to tracing…" (They did perform a lot of optimizations to get it up to speed with tracing garbage collection... however, these are far beyond what shared_ptr does.)

http://users.cecs.anu.edu.au/~steveb/downloads/pdf/rc-ismm-2...