Overall, Steam Big Picture Mode is beautifully usable. Its so well designed for a first effort it really showcases the huge difference between Valve and the traditional console makers: Nintendo, Microsoft and Sony. Sony just pushed a pretty large update to the Sony Online Marketplace and its better, but doesn't come close to the first version of...

One minor correction-- you can make a free XBox Live silver account to access the store and such. However in order to play online with others (in most cases) you have to have a gold account. It would be nice if you could hide the ads with a gold account.
More importantly, though, Big Picture mode is amazing. I have used it for my main PC, not my living room PC, and I can even see benefits to it with a mouse and keyboard. I can't wait to see what, if anything, all of these new projects Valve is pursuing are leading up to.