In so far as Russian Stealth, that is not a simple question. An F-117 was shot down, and parts of it were shipped off. However most of the plane is in a museum. Some sources claim that a B-2 was brought down, don't believe it. It is bunk, only a handful of B-2's were ever made and hiding the loss of one would be as difficult as hiding the loss of an aircraft carrier.As far as the F-117 that was shot down, I find it highly unlikely that the Russians got very much use out of it. While the Russians have proven to have an impressive capability to reverse-engineer technology (a la air to air missiles) given the sheer fragility of the Radar Absorbent Material on an F-117 (even rain can wreck it) I find it highly unlikely that anything useful survived the impact of a missile, combined with the ball of fire, and the fall to Earth.
While examining the airframe itself might seem useful, it would provide very little information the Russians did not already know. All 1st Generation stealth aircraft were based on the WW2 Horton Brothers Night Fighter. Shape is the first concern in stealth (right angles in particular are bad) So if no RAM survived examining the wreckage wouldn't provide much more than pictures which are widely available.
There are many claimaints out there that the Russians have developed a plasma-stealth screen. I have posted several points stating why this is not realisitc, and perhaps not even possible. They are in the thread titled "Plasma Stealth Bah" so I'll not repeat them here.
In new generation Russian aircraft it seems they are making greater strides toward low-observability, but stealth does not seem to be a very high concern. Why? Is debatable, maybe the Russians know how stealth works but don't have the industrial know-how to replicate it, maybe they have it and just don't see it as being worth the design compromises necessary.
Also on the F-117 that was shot down, keep a few things in mind. Number one, the F-117 was shot down because Air Force planners got lazy, and sent F-117's on the exact same path, mission after mission, allowing the enemy to know exactly where it would be. Number two it was tracked with long-wave radars which are better at tracking stealth aircraft, but suffer against normal aircraft because non-stealth aircraft create a huge return that can obscure other things. If the Air Force insisted on sending the F-117's on the same path time after time, they should have put a few non-stealth aircraft in the vicinity to obscure the radar picture. And finally while I don't have my sources on this computer (you can find them with a little googling) it is believed that the missiles that took down the F-117 had been customized to incorporate TV-guidance along with infrared, etc.
In so far as stealth, I think you will see the Russians continue to improve on low-observability, but true stealth does not seem to be a part of their combat doctrine. I have read some reports that the PAK-FA will attempt to incorporate some stealth features, but again it does not seem to be a top priority. The current docrine seems to be warfare with fast, maneuverable aircraft using very long range missiles.
Russia still lags well behind the west in terms of stealth, but they're smart enough if they make it a priority (which it doesn't seem they are) but if they do, they will get there eventually.