I know on the beta you can have 6 slots per server.
I have read somewhere that someone at Trion mentioned it was "6 slots per account" for live, but there was speculation if 'per account' really meant per account or per server per account.
I was able to make 6 characters on a server and went to log to another server when I was hit with a 2+hr queue, so I am not able to test out how many we can actually have total.
I know any sane person wouldn't need more than 4-6 slots, and I know how the souls and specs work in Rift so no need to tell me that I don't need that many "alts".
I am curious if anyone on live was able to make more than 6 characters across the realms before all of the queues started up.