This is making the rounds, a fascinating interactive map of migration using IRS data from Forbes. Note that you only get county-to-county moves for numbers of 10 or more. So what is going on for Portland? Looks like people are still coming here more than leaving here-in-migration is in black and out-migration is in red. Here is the picture for Portland (Multnomah County):
You want to see what a dying city looks like? HEre is the same picture for Detroit (Wayne County):
There is some interesting analysis at The Economist which notes that the data do not seem to support the idea that the rich flee areas of high taxation.