Maj. Dymovsky was a police officer in Novorossiysk, he recently retired from the police force and posted video clips on his website [which is no longer online] addressed to PM Putin /Pres Medvedev exposing years of corruption in the city's police.
As of now, he was on his way to Moscow to give a press conference at the Independent Press Centre, but was reportedly detained while en route to the Rostov-on-Don airport.
I read comments and most readers support the ex-policeman. Some see this is the first crack in the law enforcement system, but most simply express their support for Maj. Dymovsky. It is widely held that the situation is similar in other Russian cities, it's just that they are still waiting for a whistleblower.
Concerning Sanjuro's last point, see this Jotman post. Here's a report on Dymovsky's videos from Russia Today:
Update: More here.