I greet anyone I see on my way to my desk, but I do not seek people out unless I need to ask them something. The people I work most closely with, I will say good morning to before I ask anything about work, even if we have been in the office for a while before we speak. I don't say goodbye generally, as people are on flexitime and its not really the thing to be drawing attention to who stays later and who leaves earlier- the clock works that our and people leave quietly as a rule.