From the Dexter Blueberry Farm's email notice:
Dexter Blueberry farm is Opening Thursday July 5 2012 for you to pick blueberries.
The early berries are ready, Blue-Ray and Blue-Crop varieties. These berries tend to be larger, slightly tart and delicious. The picking will be good to excellent. By July 16 the Jersey will be ready (need rain) and they are delicious and sweet. The crop this year is huge. We expect picking to be Fantastic by the third week of July and through the season. We expect the season to last through the third week of August.dexterblueberry.com
The Blueberry Patch in Grass Lake is opening Saturday July 7 2012:
We will be open 9am-7pm, 7 days a week beginning Saturday July 7th.
Sodt's Berry Farm (Arborwiki link) also brings berries to the Ann Arbor Farmers Market.