The ODP search facility is supposed to be used for finding categories. The fact that it also returns some sites in the listings is a quirk and should be ignored.
That said, the search database is updated only every few weeks at the moment, due to other work taking place. In normal operation the RDF gets updated once per week with the occasional week missed. Search gets updated only whenever a new RDF file is generated, which takes several days to complete. So, if your site was included in the ODP after the last RDF started to roll, then you will not be in the RDF, and hence not in the search either. Allow 2 or 3 weeks after listing to be included.
The search page does include a "last updated" date at the bottom to tell you when it was last updated too.
Forum search would also have told you all that. It is a question that has been asked and answered hundreds of times before.
