Size matters not. Ie. whether you merge 100 or 1000 or 10.000 users you'd automate the process anyway in case of LDAP with ldif & some scripts. Currently used software matters (hence comparing between sites is both useless and very complex, and not necessary or productive). There are several software platforms which are 'unaware' of each other which is precisely what SSO solves (on authentication layer, that is). Question is if it is possible to implement SSO [and which SSO framework] in each software platform. Meanwhile, every framework has their pros and cons. If that is not already complex enough, imagine you're gonna end up developing code which must be tested very well because SSO is related to authentication which makes it a potential weak chain in security framework. Add to that, the developers who'd implement are professionals with limited time available. You can read the discussions here: http://wiki.maemo.org/Task:Single_sign-on http://maemo.org/maemo-meeting/sso-m...009-05-27.html Write less, read more, thank you.