The search data is updated about once a week, but due to ODP down-time over the last few weeks, search has only been sporadically updated. The Last Updated date is shown on the search page each time.
The dmoz search function is mainly used not to find sites, but to locate Categories. It isn't much used by the general public, most of them are using data on Google and AOL, and others, not dmoz. The ODP is not a search engine, it is a directory, so the major results of a search are a list of categories. Once you have found the correct category, you have a list of similar and related sites, with a directory tree structure to jump to related categories. This is how it is meant to be used. However, a few sites are returned in the search results, but that isn't the main purpose of the dmoz search function. You will notice that the ODP does not "keyword stuff" the Titles and Descriptions; we do not optimise your site for search engines, we just list sites, but within a directory tree that makes it easy to find a bunch of related sites by browsing the tree, not performing a search. The search is mainly used by editors attempting to find the best home for a misubmitted site, and anxious webmasters looking to see if their site has been listed yet.