Pine straw in and of itself is acidic but as it decomposes and gets mixed in with the soil, as with most compost, it does revert to a more neutral pH.

Peat, added to the planting hole for the blueberry bushes, and mixed in with the surrounding soil can acidify the soil mixture. Sulfur is another commonly used soil amendment to acidify soil - both more effective I think than pine straw at getting the pH down into the 4-4.5 range required. And, whichever one you use has to be renewed annually or more often to keep the soil in that range.

Another alternative is growing them in a raised bed or large container where you can create naturally acidic mix to begin with. That is what I do as our native soil is so alkaline I'd never get it acidic enough.

But first, if you are going in-ground, you need to know what the pH of your soil is before adding any amendments. A professional soil test done by your local county AG extension office is the best place to start. The article linked below gives some great details on soil preparation for growing them. Hope it helps.

Good luck with the blue berries. ;)

dave

Here is a link that might be useful: Growing Blueberries in the Home garden

As digdirt stated while pine straw will test, when you crush some of the needles into distilled water and let it sit for at least 24 hours, somewhere around pH 3.5 once the soil bacteria start to digest it no affect will be seen on the soil. To change the pH of your soil you need to cahnge the number of free Hydrogen ions floating around there and to increase those the best way to do that is to add sulfer which helps bind the oxygen ions so they cannot combine with the H ions.
In my experience I have not seen that adding peat moss to soil does any more to actually change a soils pH that any other organic matter, and adding a 3.8 cubic foot bale of peat moss to a 4 x 4 garden plot caused the pH of that soil, a year later, to rise from 5.7 (what is was before the addition of the peat moss) to 7.2.