The proper Bolshoi Theatre has been under renovation since the summer of 2005, and was meant to be finished in March 2008. According to the Moscow News from the beginning of 2009: "In the past few months, no one was willing to risk a prediction on an official opening date, and some people even said that the work could drag on for several decades. (Russia's Minister of Culture Aleksandr) Avdeev, however, reassured the public that the Bolshoi renovation would be finished by the end of 2010."
So, at the moment, the Bolshoi company performs ballet and opera in the theatre next door. We went to see Tosca (seats 750 rubles/£15) which was a great romp with plenty of drama and volume. I do feel a bit a cultural snob about the staging though. There was a lot of very literal interpretation, much hand-wringing and - what seemed odd to me, although I know almost nothing about opera - a liberal slavering of religious iconography, including a life size crucifix and a smoke ring halo over Mario as he gets shot (sorry, given the story away). Is that in the original?