It seems like a superficial tabs-versus-spaces kind of point, but when you see how the standard library is organized and how package names interact with actual programs, you grok why underscores make people wince; "foo_bar" should either be "foo/bar", or just plain "bar".

The import statement at the top of the file can clarify what the origin of a package is, but in the program body itself, the package name should make the library feel as natural as "fmt" or "io" or "math".