Last I heard they are really good, at least the Sims team was. But that was a few years back, havent talked to anyone since. They had the ability to basically pick a date and build the game from there.
Its not so much that the build is compiled, but that they can compile it at will. Who knows how long EA keeps the archive, but I havent heard as many complaints about them as I have other companies.
I dont have any details but I heard some rumors that the source code to older games in the C&C series has been lost or gone.