I installed it even though I consider myself a careful user/player/surfer and a reasonably competent sys admin. However, all it takes is missing one security patch, hotfix or update with a threat in the wild and you can be hit.
I was keylogged once because my java version was out of date for whatever reason and an exploit scripted into a sidebar ad on a gaming site installed a keylogger. Had I had an authenticator the keylogger woudn't have been useful to the black hat that cleaned me out.
So I think to poo pooing the authenticator because a user "knows better" or has "never been hacked before" is hubris and short sighted, especially when they dangle a carrot of in game items AND offer a free version of said protection.
Installed on a B&N Nook Color running CyanogenMod 7 08112011 NIGHTLY-encore.