Fixed 30 year mortgage rate?

I would like to know if how much do the 30-year-fixed-mortgage rate varies from bank to bank? Given that: 1)I have already been pre-qualified for a loan, 2)There is incentive (0.5point back towards closing cost) from preferred lender from my builder Should I bother to shop around to see if other banks would beat out [...] http://bit.ly/kprWQE