I find myself in the weird position now where I get way more email from people than I could ever answer and still do everything I need to do. The way I get over my guilt about not answering email is to hold office hours. Once a month, I make myself available so that anybody can ask me anything on my website, and I try to give thoughtful answers that I then post so anyone can see. You just have to be as generous as you can, but selfish enough to get your work done.
