I know people are busy. I am too. And I don't assume everyone will be waiting for my email and send back a reply in less than a day. I don't mind if I have to wait. As long as you know the reply/answer will come around sooner or later. Walking up to the person or calling him/her helps of course, if possible.
So, how do I handle email? I basically apply the Getting Things Done rules: if I can answer within 2 minutes, I reply right away. Most email fits in this category... If it takes longer I plan it in my calendar and tell the sender when I'm going to answer. You can do that in 2 minutes as well.
How do you handle this? Do you recognize it?