The clarification is that this is happening for all users, not just Russian users. That is, if you're from Moscow and you're in the US, you get your userpics from San Francisco. If you're from San Francisco and you travel to Moscow, your userpics come from Moscow. This is purely a speed enhancement, since the majority of things that your browser downloads are public, static files.
All other data (blog data, public and private entries, large photos, etc), will continue to be stored and served from San Francisco as before. Blog URLs aren't changing either.
Really, there should be no noticable difference to you except improved speed. (because pages finish loading faster, since the majority of components on the page load quickly from Moscow, if you're near Moscow)
However, because you may notice that these public files now have different URLs, we wanted to let you know what's going on.
We hope you'll enjoy the improved speed!