If all it takes is a reply to an email or a note added on their site that I received the request and can meet their ETA, I am happy to respond. If I have to print out an attached form, enter the ETA by hand, and fax it back to the client because the request for status and ETA came from an email account that does not accept reply emails, it is usually ignored.

If vendors need to know that I received a search request and an ETA, it helps to make the ability to respond as quick and simple as possible.