What is your definition of SSO in this case (in terms of user management and creation)?
SSO is supported (in a sense) if a user creates an identical logon and same password (at least is does with AD integration - I assume it would be the same otherwise). However, user accounts have to be created in each portal. In the latest release, the core team changed the use of teh ASP membership tools, greatly simplifying some of these issues. Extending users to other portals is now much easier behind the scenes in SQL than before.
I'm sure there are many more changes than that, so you'd have to read up further on those in blogs and other spots (I'm still reviewing changes and trying to understand it all). For my organization, I prefer multiple portals rather than pages/page sections for different departments. However, we run the risk of users not logging in on all portals, since they have to log into each portal at least once before the transfer across portals works. The only way around this, is to copy the user info to the other portals as created - which as I said, is MUCH easier now after the membership changes.
(e.g. simple entry in UserPortals extending an existing user to a new portal allows logon to be seamless, but you really have to do more tthan that if you want roles & assignments extended as well)
I hope this provides some insight into your query, but you should setup a test install and play with this yourself to see the ins and outs of it all.