Ok - in truth I cannot be sure it was working before the upgrade - I had no reason to check. It is not working now.
In the Site Settings, User Profile points to the home page. When you click you display name on the site it takes you to the home page.
On a site freshly installed using DNN6 I find that in the site settings User Profile points to a page named User Profile. On that page there are two modules, one ViewProfile, the other Messaging.
Neither of these modules is present in the upgraded site. I'm pretty sure that nothing went wrong in the upgrade, how are profiles meant to operate in an upgraded site?