The blacks always vote for whichever Democratic candidate is on the ballot in the fall by about a 9-1 margin.
If Obama is the nominee, it'll be a little higher than normal, but this is nothing new.
IMO, the fact they they identify with a particular party year in and year out is the reason why Karl Rove has spent the better part of his recent career "caging" black voters.
He wants to make sure as many of them are disqualified BEFORE Election Day as possible. This also was a key factor in last year's U.S. attorneys scandal which resulted in AG Alberto Gonzales' eventual resignation.