Heads up - where is the best place to send feedback for little gotchas like this:
mbar:src shephard$ sudo go get code.google.com/p/go-tour/gotour
Password:
# cd .; hg clone -U https://code.google.com/p/go-tour
/usr/local/go/src/pkg/code.google.com/p/go-tour
package code.google.com/p/go-tour/gotour: exec: "hg":
executable file not found in $PATH