Single Sign-On and all that

This is really not so much of a post, as a link to a basic overview of enterprise single sign-on (ESSO or SSO) that I put up on the Squidoo site a little while back. So before I go too far, here's the link:

The (Unofficial) Executive Guide to Single Sign-On

So what are the lessons to be learned from the article. Well, firstly, that there's a fair bit of background to consider before we even get to single sign-on in a business environment. Things like existing directories and authentication methods are critical. As is the way any SSO integrates with these. There's also the consideration of applications. Typically web and client/server apps are pretty simple to SSO into. Legacy apps using emulation can create challenges, as can Java apps with multiple libraries. None insurmountable.

I'd be interested in your opinions on SSO systems you've used. From any of an implementation, administration or user perspective? And whether it's been part of an all-encompassing identity management project, or focussed SSO project.