What does Google do with 404'd duplicate pages on another site?

[internetheaven]

If found a site duplicating my content, they have removed it and all the pages that my content were on now show 404 headers.

BUT - Google says that it never really gets rid of pages that are removed from the search engine results. So is there now a record of hundreds of pages in their index showing my site has duplicated content on the web? Are pages removed from the rankings still used to help the ranking algorithm?

Would I be better demanding that the offending party put up new content on the pages in question rather than just removing them? i.e. Google indexed new content at those pages and forgets that they were duplicates of my site rather than just putting them in their "removed" index.

Thanks
Mike

[g1smd]

Whether they put new content up or just return a 404 for those URLs, Google usually hangs on to the old data for at least several months.

Personally, I don't think that it matters either way.