I wonder if there's another way to solve this problem. For example, a plug-in that would store cookies as opposed to passwords - and then "populate" a new session with existing cookies to log you in transparently.
More of a security nightmare than passwords? Maybe, though I can't see why...
Anyways, yeah I thought about binding auth cookies to some kind of persistent hash, although I'm not sure what it could be... IPs change (laptops moving), so do user agents (browser upgrades)... I guess I'll need to test this!