This move was expected after LB Matt McCoy collided with Aaron Curry while covering a punt return, and his knee was bent in ways it shouldn't bend. David Vobora and Matt McCoy are of similar makeups, experienced linebackers (Vobora has 16 starts to his career) that are expected to contribute primarily on special teams. McCoy was purely a special teamer with the Bucs, but also played nickel linebackker for us.
On nickel downs, McCoy was generally asked to stay close to the line while the other linebacker (Curry or Hill) roved more. Vobora played strongside linebacker with the Rams, and I suspect he'll take over McCoy's role without too much of a hitch, though it's not unthinkable we'll see Leroy Hill and David Hawthorne in as nickelbackers or on rotation. Regardless, we're at an advantage here for having had Vobora with us in the pre-season, which should make the switch from McCoy to him much easier.
There has been no official word on McCoy, though the injury certainly seemed season-ending. We'll wait to hear if he is to be put on Injured Reserve or if another move will be made to free up the spot for Vobora, but I'm guessing he'll go to IR.