A lot less. At 3% inflation $1,000,000 is equivalent to $411K in 30 years.
That said there is a lot of crazy turmoil in the muni market, due to the problems of MBIA, and other bond insurers. This has widened the yield differences between Muni's and treasuries to historically high levels. The studies that have come out recently seem to show that the default risk of a relatively low rated Muni A or BBB are in reality closer to a AAA corporate bond.
I also think that odds are very good that we will see a rise in top tax brackets, and/or the tax rates capital gains, and/or dividends. All of which wil make Munis are relatively more attractive in coming years.
I think having a $1 mill portfolio of muni consisting of 20-40 individual issue and staggered maturities as major portion of your retirement income, might make sense in some cases. Obviously you wanted to have a additional taxable income in order to benefit from owning munis. I think you'd also want to construct the rest of your assets to be pretty inflation resistance (e.g. Real estate, maybe commodities, and equities.)