The official dates for the Carnival 2008 go from the 2nd to the 5th of February.
Still quite far way in time, though early birds are already making enquiries about accommodation.
For the time being there is no official information on either the Rio (Rio Turismo) or the São Paulo carnival. The carnival industry in Salvador seems much better organized, you can find more details on the Carnaval there (it begins on 31st January) at Central do Carnaval and at É Folia.
As more details emerge, I will keep you posted.