Also note that you should only be doing this as a convenience to the end user - you can not depend upon this value not changing. The end user can bypass any "read only" type restrictions you place on the data, thus you can't assume that it will be unchanged when the form is POST'ed back. If it really matters to you that the data remains unchanged, keep it (or at least a copy of it) on the server side of things (such as by using a session).
