Who needs Google Ads when you have the Catholic Church?
Now, first a disclaimer. I do not intend to see the Da Vinci code, and I personally do not like to test God concerning works of fiction based on Biblical word. However, the First Amendment should still be upheld, and I am rational enough to know that rioting in the streets will not accomplish anything (apparently, pictures of some prophet are justification for irrational violence).
That said, the public boycott by the Catholic Church should be an example. Instead of keeping people from the theatres, it only serves to make people more interested. The Da Vinci Code had one of the strongest opening weekends ever. So much for making The Da Vinci Code look bad; the Catholic Church should have left that to the critics, who indeed have been very disparaging towards the film.
Boycotts, in general, are ineffective. On May 1st, protests were common for Illegal Immigration Day; the effect on the national economy was minimal, even considering the numbers who participated. E-mails have spread suggesting that certain days be designated to not purchase gas as a symbol to the oil companies. The hope was that a large drop in daily sales would bring a sharp drop in prices. However, the oil companies likely are aware that if people do not buy gas one day, they will the next. Many people simply need gas to get around. And most other boycotts are so small that they could never hope to make a significant impact.
I am not going to say that rallies and protests do not do anything; on the contrary, they can be very effective. But a poorly chosen form of dissent (like say, oh, having 17 students sit and whine in a state building) will only work against the cause.