I'm pretty much in the same camp as Folke. I don't need a special view. But I thought I have read other postings where users have a desire to review their Completed Tasks to assist them in compiling progress reports their employers might require.
One idea for a special view is to put a "Complete Tasks" view under the spot where "Area" "Tags" and "Archive" reside. I suggest showing all the non-archived completed tasks. Completed Tasks already exists under Projects & Actions, but are intermingled with non-completed tasks. Since you track the date/time of the Completed Tasks, an option to sort them in descending order by Date/Time would allow me to see what I inadvertently marked complete. It should also help those who want it for reporting purposes as well.