After spending some time with Big Picture on a TV using Windows over the month, I've been convince that this is a waste of time. A PC will never match a console like experience.
If you want to play multiplayer games that has camera base action, all it takes is for someone to be sitting at their desk using a mouse with a stupidly high poll rate to crush any controller, and that's just the mouse; you include the keyboard and it's obvious. Even though there are titles that includes auto-aim support for e.g. the latest Call of Duty games, I question "why then compromise the experience for those at the desk?".
Ok, well, lets stick to Co-op multiplayer games then. In Left 4 Dead 2's case the UI is incompatible at the couch since you can not chat with desktop users. Maybe we will see some sort of standard with Steam couch in-game texting, who knows.
Now, here is where Big Picture shines, single player games, it works : ) Well, some of them. Remember there are single player games that ships with multiplayer features which goes back to my earlier reasons..
I'm not even going to dive into the software bugs, there's a laundry list of them.
Valve basically forgot the whole point of the couch which is comfort.