There may be too many programming languages in the world for them all to be taken seriously but Google's Go has the advantage of Google built in. Now it has graduated to be one of the languages you can use with the Google App Engine.
Java and recently Python have been added to App Engine but you need to notice that Go is still marked out as "experimental". In this particular case it is App Engine that is doing Go the favor rather than vice versa. To have a real target environment is a big advance for Go and one that might just increase its user base from enthusiasts to programmers who are actually trying to achieve something. The attraction of Go is that as a young language it doesn't have the layers of accumulated frameworks and code that makes everything seem more complex. Of course this lack of wide support is also the languages disadvantage as you have to reinvent a lot of facilities from scratch.
The App Engine uses the new 1.5.2 SDK which is not backward compatible and existing apps may require changes before things work properly. Notable by its absence is Windows support - the SDK works on under Linux and Mac OS. This also reflects the lack of official support for Windows for the language itself. So if you want to use Windows with App Engine you have to use either Java or Python.
What does the future hold for Go?
It's not a remarkable language but it does have one or two good features. Its two biggest problems are that it doesn't take Windows seriously and Google seems to be in a state where things that don't perform are being closed down without much compassion - see:
Google Labs to close,
Google retires PowerMeter and Health,
Google dumps APIs.
Google App Engine Go-es Forward
Go with Google - Yet Another Language!
Getting started with Google's Go