The result above - where #crapdatingagencies is both a trending term and an empty search string - is most likely a technical fubar rather than Twitter censoring the results to protect brands.
However; this result does also illustrate the rising importance and demand on instant search. As Twitter offers us instant market intelligence we also become more needy of it.
What may happen with this trending term is that - all of a sudden - the block will clear and Twitter will start to name and shame a host of online dating sites. This is a competitive area with sensitive brand concerns. When it comes to online dating the "wisdom of crowds" is king.
This is also the second #crap-- trending term of the day. On Twitter we've also been having fun naming #crapnamesforpubs. Only time will tell if #crap-- trends become a stable but if they do then we'll see a rush on account names and even domain names.