In response to a suggestion by none other than Mr. Daniel Brandt, I've just added a new META tag to the board's global headers, to help prevent the unwanted caching of Wikipedia Review discussion threads and posts that have been deleted or (more likely) moved into non-public forums.
This should begin to take effect immediately, and will become increasingly noticeable over the next 2-3 weeks, as existing search engine caches are cleared to (hopefully!) respect the new tag. Within a month or so, there should be few, if any, "cache" links remaining next to WR page listings in Google and other caching search engines.
We're sorry if this causes any inconvenience for, well... let's just say "certain people"!
Someday I also hope to make it possible to prevent crawling of individual threads, or even individual posts - and if feasible, the automatic substitution of specific character strings in posts for crawlers only, based on internal BBCode tags. (These ideas are similar to suggestions I and others have made to reduce the "search engine footprint" of specific "attack" pages on Wikipedia.)
However, those innovations (unlike this one) will have considerably greater overall impact, and will therefore not be implemented without discussion in advance.