Communication: No news is bad news
It's been my experience that, most of the time, delayed responses are bad. If I ask a question, and don't hear back from someone soon, it usually means the answer is negative.
In various psychology classes, I remember learning that people tend to give positive answers quickly, but are reluctant to say "no". This was noted as especially true in Asian and Indian cultures.
That said, there are a few exceptions: People going on vacation, not getting the message, emergencies coming up, etc.
In general, if I send a request and don't hear back within 1-2 business days, I assume about a 90% chance of some sort of negative response.
Does anyone know of any empirical research on this subject? If so, please post it as a comment.