Currently -- if you get a contact form, the store email is in the Sender field, so you cannot simply "Reply" to the email, you have to cut and paste the email address of the customer. The customer's email address should pre-populate this field.

I'd also like to see the customers email in the "from" for admin order confirmations.

We follow-up (or try to) on each order and have had this feature on the other shopping carts we've used. Not having this makes the follow-up process much more time consuming and prove to error.