>Postgres contains a built-in function that
>computes whether a geometric object contains
>another geometric object.
PostGres/PostGIS is can't be used because of project constraints (no complex db servers, etc.). Nevertheless, been there, done that. To really use the PostGIS functions (I am on that mailing list), I have to take account of other issues such as correct projections. Makes the task more complex than I need it to be. And, it is not an easily portable solution.
In any case, my testing shows that speed is comparable to what I have above.
when small people start casting long shadows, it is time to go to bed