bug: with apache 2, apache_lookup_uri("/directory") spits out a warning and fails to return anything.  apache_lookup_uri("/directory/") works.
another bug: virtual("something") forces a header flush.  I know it's documented, but it would be rather wonderful if it didn't do this.  You never ever want to flush headers when you're using virtual() to include a dynamic file such as a PHP or Perl file, which excludes virtual() from being used on most of any website's contents :-(.