Code quality of the service they were offering:
It's improved a little recently but search is still bad, the shared document function was very buggy and made material disappear. General bugs and niggles in past.
Search is hard. Google has the benefit of getting a lot of training data. Corporate intranet search, searching your documents, etc. has to actually figure out relevancy and can't infer it from having already served that query thousands of times in the last day.
