Contributors Summit – The Go Blog (blog.golang.org)

    To make critical fixes to packages in the standard
    library, one must wait 6 months for a new version
    of Go to ship (or a point release has to be shipped
    in the case of security issues, which drains
    team resources).

I realize the article suggests breaking more functionality out into external projects to get around this, but I'll also advocate for a shorter release cycle. 6 weeks makes more sense than 6 months, IMO. I'd be curious to hear arguments for the long cycles though, as so far I haven't been convinced.