by andreas@ionisiert.de:

What steps will reproduce the problem?
cd
rm -rf go
hg clone -u weekly https://go.googlecode.com/hg/ go/
cd go/src
./all.bash
go get code.google.com/p/goprotobuf/{proto,protoc-gen-go}
package code.google.com/p/goprotobuf/proto
        imports code.google.com/p/goprotobuf/proto: import "code.google.com/p/goprotobuf/proto": cannot find package
package code.google.com/p/goprotobuf/protoc-gen-go
        imports code.google.com/p/goprotobuf/protoc-gen-go: import "code.google.com/p/goprotobuf/protoc-gen-go": cannot find package

cd code.google.com/p/goprotobuf/proto
go build
go install
go install: no install location for _/home/aj/go/src/code.google.com/p/goprotobuf/proto

What is the expected output?
go get should work / fail with an error message pointing to the source of the problem.

What do you see instead?
a cryptic error message.

Which compiler are you using (5g, 6g, 8g, gccgo)?
amd64

Which operating system are you using?
linux

Which revision are you using?  (hg identify)
weekly 2012-03-04

Please provide any additional information below.

source of my problems: I had GOPATH set instead of GOROOT.
fixing that now everything is fine. but the error messsage doesn't
help to find out what is wrong and migth confuse new users.