ODP has a general policy for content that it will and won't list at
http://dmoz.org/guidelines/include.html
There are various types of sites allowed (sometimes only in specific areas), and the description of these is at
http://dmoz.org/guidelines/site-specific.html
I mention the above links to help you decide if you've spotted something which doesn't belong.
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Some sites (usually companies) change their content over the years and the descriptions and category locations have not kept up with the changes. Point us to those listings, and we'll re-review the site.
Some sites are blatant, money-making HIJACKS. Someone's domain expires and is snapped up by those who are trying to get people to visit casinos, porn sites, ebay, "distance learning" sites, shady pseudodrug sites ("herbal viagra!"), a nice-looking PPC (pay-per-click) directory or whatever else can make someone a few cents or bucks. Sometimes the intent is just linking trickery hoping to get Google to make a site jump to the top for some term or phrase. In any case, we want to know about all of these HIJACKS -- especially those which are PORN in a non-adult area of the directory.
Sometimes a company buys the URLs of other companies (or even nonrelated URLs) and then redirects you to or mirrors their site. This is a type of directory abuse typically practiced by those wanting multiple listings - although it could be entirely inadvertent. Tell us about any MIRRORS you see and we'll rereview those sites ASAP.
Finally, there is the ol' BAIT AND SWITCH. Site owner gets listed, says "yippee," and then goes and changes the some or all of the content to something unacceptable. Others are sneakier and decide to serve up some "nice and appropriate" page for those coming from dmoz.org (who are usually editors) but a "cruddy and otherwise inappropriate" page to everyone else, the public. We want to know if you ever find any sites like these.
You can report DEAD DOMAINS here as well as those which seem to be placeholder pages ("Coming soon!") since they're likely candidates for hijacking.