En route Controller voiced concern regarding the over reliance on URET information as it relates to possible missing aircraft; noting controllers are too reliant on automation for information.

Narrative

A C206 was in URET but showed (unk) for the controlling sector; signifying he was probably in an Approach Control. He was projected to be in Center's Sector X and I saw a VFR target at the approximate position he should have been if the URET projection was accurate. But he wasn't 'overdue' in my sector yet so I waited to see what developed. Time passed with no news and the flight plan was projected to be in my airspace; so I called the preceding sector (Center-X) to inquire about the C206; Sector X didn't know anything and called the preceding facility. The Sector X Controller then learned that the pilot had terminated flight-following with Approach and so he removed strips on the flight plan. An important note: at no time did the flight plan show overdue in URET. When aircraft do not appear when they are expected; controllers should be concerned. The critical first step: be aware they have not appeared. The implementation and use of URET has made controllers more reactive to flight plan management; and caused heavy reliance on URET notification of overdue. When you rely on a machine very much; it must perform very well. Since the C206 did not show overdue in URET; he may have crashed in a kudzu field and nobody would have known anything was wrong and nobody would have looked for him. Controllers must be taught to distrust the URET and have an investigative nature; it is a good tool but it has many flaws. Of course a big first step to eliminate this type of situation: when an aircraft terminates flight-following or cancels IFR; remove strips. Approach failed to remove the flight plan. But it shines a light on the more serious problem we have in initiating timely search and rescue.