Such an interesting discussion... I am following it, but I haven't got much to add myself. Just interesting to read the responses! Thanks Iorka, for answering each one of my questions separately.
The modern situation with religion in Russia and the ex USSR is really rather contradictory, I think.
One thing that nobody mentioned is that perhaps one of the reasons many are religious today is that things genuinely were very volatile and hard for many, particularly in the 1990s. Perhaps some turned to faith for the first time in their lives during this period, and remained religious since. A Russian woman told me something to that extent, although I am not sure I understood everything she said perfectly, I might have misunderstood.
On what to do in a religious service which is not your own branch of Christianity.... I think Throbert takes a very uncompromising stance! It is quite possible to just play along a bit. I don't see how any of us who actually do have faith can be 100% certain that the particular denomination we were born into is the right one. I wouldn't take communion in a Catholic church because it might offend some serious Catholics (I am Lutheran).
Orthodox Christianity seems even more ritualistic than Catholicism.... You really have to know what is about to happen and what to do to follow along! I got very self conscious about not walking into churches without covering my head, when I was in Eastern Europe. It just felt a bit insensitive, both to the locals and possibly to God (it's actually in the Bible).
My final comment is about Stalin. In many ways he seems to have been the least "orthodox" communist of all the Soviet leaders. He just went ahead and did as he pleased, without worrying about what communist doctrine would have to say about his plans. For example making religion acceptable again during the war. In this particular question I think he was right though.