Update on Gazeta.ru's earlier report about Minsk center having been cordoned off: no, it is not, according to this post in the Minsk LJ community.
As proof, a link to a live webcamera in Minsk.
Another update: Ukrainian Channel 5 reports that streets leading to Oktyabrskaya Ploshchad - where the opposition plans to hold a meeting at 8 pm - are indeed blocked. (I now have a TV in my room - thank you, Mishah!!! And I'm pretty shocked by the bullshit commercials of the Regions of Ukraine Party... Later: Well, all of them are sort of sickening, actually...)