I don't really know Go except for like 5 min of reading up on its syntax, so I could be wrong, but this assertion that it was not obvious how to write to a file in the documentation surprised me. So I clicked on the stackoverflow link.

OpenFile returns type File from the signature. http://golang.org/pkg/os/#OpenFile

Scanning through the methods (or doing a cmd + f search for "disk") has this method http://golang.org/pkg/os/#File.Sync

Method description says "Sync commits the current contents of the file to stable storage. Typically, this means flushing the file system's in-memory copy of recently written data to disk." Isn't that what you want?

Was it as clear as the C# example? Probably not. But I don't think this was terribly hard to find. Code examples will come in time, as the language matures.

IMO whether to put code examples into the documentation is really a choice by the language maintainers. Lots of code examples can also clutter the docs. I prefer to just have the docs tell me what each function does. If I really get confused, I can google for examples. Java also doesn't really have code examples right in the documentation, but they aren't hard to find because it's been around for a long time. For example, Googling for "java code example how to append to a file" and click on the first link.