There are some photos
here. The guy on the right in the little kiss-in in the first photo is my newest addition
ilupin (his blog is in Russian, but he understands English). He isn't one of those who got arrested.
My translation of the Russian text:
7 April: Participants in a picket against the law on gay propaganda were arrested in St. Petersburg
A protest action against the law prohibiting propaganda of homosexuality was held in St. Petersburg. The protesters timed it to the International Day of Silence. They came to the area at the Oktyabrsky Concert Hall with signs, with their mouths taped. Two picketers were arrested.
The first arrestee was the chairman of the interregional public movement "Russian LGBT Network" Igor Kochetkov, who had raised a banner saying "There is no hushing up crimes against gays and lesbians!"
The second protester was arrested for holding a sign saying "A friend of our family is a lesbian. My wife and I love and respect her. Her lifestyle is as normal as ours. And her family is socially equivalent to ours."
UPDATE:
Here is a more detailed (but not very long) report in English.
This was the second round of arrests for a protest again
that notorious law in the city of St. Petersburg already. You can read (in English) about the previous arrest on 6 April
here in Pink News, and here is a Reuters video of it: