99USD/year is too much.
For four accounts??? Goddamn everybody wants everything for free.
It's actually "up to four accounts," and it's not clear how they'll be limited. If it's just a four-pack of yearly codes, super. I suspect it will be implemented in a way which prevents people from using it across disparate locations and saving money by dividing the 99USD four ways. (I just read am nintenho's post.)
As for "free," I actually think that a single, logged-in Gold account should enable access for any other currently-logged-in Silver or Non-Live accounts on a single machine, limited only by any game's features and any other DRM in play. So if a game supports splitscreen multiplayer and online simultaneously, and one player is Gold but the other Silver, they should still be able to play an online match against others. However, if the Silver account initiates a download, it would still be limited by the parameters of his account.
This actually came up for me when trying to use Video Chat, where I logged in and was talking to my sister in the USA. My wife wanted to talk at the same time, so I pulled out an extra controller and headset, and turned them on. It wouldn't recognize the other controller's mic, so I logged in my wife's Silver account. The 360 ended the Video Chat without warning or explanation. It wouldn't allow me to restart the video chat until I'd logged out her account. It pissed me off.