My understanding is that Go has a very simple optimizer. They were waiting for all the C code in the compiler to be translated to Go, which I believe was done in the last release.
not an expert, but i think you are talking about Go's garbage collection, which i don't think is an optimizer.
Some improvement to the garbage collector was done in the last release, and involved moving much of the runtime to Go. Making the compiler into Go, however, is actually only completed in the 1.5 (development) branch, to be released in... August, I think. That'll open up the work on the optimizer (and everything else in the compiler) to be done in Go.