I usually do, as long as the e-mail requires an answer, and as long as the return e-mail address is valid!

If you want an answer, be sure that the reply address is a good one. I regularely answer e-mails and my answer gets returned because of non-existant destination e-mail address. Sometimes it's just a comment, but sometimes it's a question about the stories or the registration process, and whoever sent it might think that I don't give a damn because he/she never hears from me.