Since Google's results are always cached, this search will return deleted threads/posts. that could be a bit inconvenient, since clicking on such a result will of course lead to nowhere.

don't know how involved it would be to check the result against the current state of the db... i guess that would probably render some of the advantages of google (fast results) obsolete...

edit:
a page saying that this item has been deleted would probably help. at least people wouldn't be encouraged to write the admins (like they are now )