Many people here mention the culture as important factor, and suggest using other higher barrier communication means. Funny thing is that as a manager I am trying to push for emails instead of drop by’s in person, as emails at least give me the freedom to choose when to process them in batches (and leave a trace in my memory). And it seems that in my culture (Russia) personal drop by’s have the least barrier, immediately followed by the IMs, while Email has the highest barrier.