Ever since I heard about google's new language Go I wanted to use it for microcontroller programming. In particular Atmel AVR micro-controllers like the Atmega series. Is there a Go port for this architecture?
No there is not. See http://golang.org/doc/install.html
Go compilers support two operating systems (Linux, Mac OS X) and three instruction sets. (amd64, 386, and arm (a.k.a. ARM))
I do not thinkg that the purpose of Go (multi-core/highscalability) goes well with mikrocontrollers.
Go ask yourself why C (and even assembly) is preferred over C++ on micro controllers.
I may be answering too late, but Go, as August of 2012, has both the default compiler (6g, 8g) and the GCC compiler (it's actually official, too, but not the default), which means that it supports all the architectures that GCC supports; however, and as Limbus stated, Go is addressed to multi-core computers. I personally think that you would get better results with C. If you still want to use it, that is going to be fine, since Go manages well in single-core applications (but not as well as C).