In a series of posts on the Oregon Office of Economic Analysis blog, Josh Lehner explains in great detail where the new residents of Oregon are coming from and just where they are going.
There's a lot here to consider, but HFO's reading is:
Southern Californians are the largest set of migrants to Oregon (L.A./Riverside & San Diego).
Portland is getting in-migration from all big cities across the country with NY ranking #3
There is a slight net migration gain to Seattle from Portland.
82% of people leaving Portland for Washington are moving to Clark County... (tax reduction, anyone?)
People leaving Portland move largely to Seattle, Austin, Houston, Denver, Charlotte, New Orleans and Dallas.
See more cool charts on the state's economic blog.