I think I would originally have said that I don't care if it's in the employment contract, as long as the goals set for me that affect my evaluation are clearly spelled out. In other words, I don't need all-encompassing descriptions of what I do, as long as I get time to do the important things, and we (me + management) have agreed on what those important things are.

However, it would be nice if my job description actually listed all of the things that I actually do, so I could get credit for them when I move positions. It would also help to backfill the position. Perhaps all those crazy DBA postings that do way more than a DBA should be expected to do have evolved from people doing "other duties as assigned"? If every job actually listed what we do, more people might realize what is acceptable?