I used to play the Caro-Kann a lot as black. One line that I reached many times in advanced variation is:
1. e4 c6 2. d4 d5 3. e5 Bf5 4. g4
In this position I saw one game where Anand played Bc8 and in my experience this line is very solid. The move Bg6 suffers some pressure from the pawn sacrifice e6, when the development of the bishop on f8 becomes difficult, and white easily controls e5. I saw one game Topalov vs Morozevich where Morozevich played Bg6, but then Topalov did not commit himself with e6.
My question is: should the pawn sacrifice e6 be feared?