The folks promoting Killzone have created a toolbar game: a Firefox (or IE if you really must) toolbar add-on, which layers a simple time-crisis style shooter over your usual browsing experience.
At first, I didn't really work out what was going on: my toolbar said, YOU ARE UNDER ATTACK! but nothing happened, so I carried on clicking about. Then, mid-browse of New Tee Vee on an Escapist thing, my browser "hung": LOADING KILLZONE... PLEASE WAIT.
...and I disabled the toolbar, because I really wanted to go read the Escapist, but as promos go, this is pretty cute.
You can even play in Squads...
I wonder how much it cost, and how long it took to develop? I wonder what else add-on games can do, other than PMOG?