The Google response ("go pound sand") was actually better than the Yahoo response ("Your site has been manually removed from the index.")
The cloak is easy to spot.
1. Find the offending page in the SERPS.
2. Click on the Cached Version to see the page which is on your site. That is what Googlebot saw and indexed and ranked the page based on.
3. Click on the SERP link to see the porn gateway page on their site.
4. Complain to Google.
5. Get told that they do not care about content on pages and there is nothing wrong with this practice.
6. Complain to Yahoo.
7. Get told your site has been removed from the index and will not be returned.