Google started to filter search suggestions that include terms connected with copyright infringement like "torrent", "bittorrent", "rapidshare", "megaupload". It's a greasy slope and Google's suggestions will be less useful since they'll no longer comprise many popular searches.
Last month, Google explained that this is one of the changes future to address copyright infringement. "We will prevent terms that are intimately associated with piracy from appearing in Autocomplete. While it's hard to know for sure when search terms are being used to find infringing content, we'll do our best to stop Autocomplete from displaying the terms most frequently used for that purpose."
Blacklisting keywords like "torrent" is a awful way to prevent copyright infringement since users can forever type queries without Google's help. The main result is that Google will appear to be broken and users will no longer trust the suggestions because they're suppressed. Last year, Google started to become politically correct by removing the suggestions for queries like [why are muslim]. There will forever be complaints about the suggestions, but starting to randomly blacklist keywords opens a can of worms and makes it easy to remove other contentious suggestions. As Mashable says, "this is a subtle form of censorship, and at first look it seems trivial. However, even though the censorship is slight, it still indicates Google's willingness to change its search protocols to satisfy the needs of a convinced business group, in this case members of the entertainment industry."
Google doesn't blacklist "pirate bay", "isohunt", "mediafire", "cracks", "serial numbers", "keygen" and there's a simple trick to bypass the obtainable filters: start your queries using the blacklisted keywords (for example: [torrent ubuntu 10.10]).