I don't like that I need to make separate accounts for Stack Overflow, Meta, Server Fault and Super User. I would like to sign into all of them with one single account. Reputation and badges should be different on the different sites, but display name, website, location and age should not.
I prefer to keep separate accounts on each website.
Each website serves a different purpose. I intend to to keep separate profiles appropriate for each service.
See the Accounts tab on your user profile to link accounts.