The millage in Multnomah county rates range from $14 to $20 per $1,000 assessed value. Assessed values cannot rise more than 3% per year.
A recent article in one of Portland's alternative newspapers touched on this very subject.
Here is State's property tax page: http://www.oregon.gov/DOR/PTD/IC_303_670.shtml
In addition to Oregon Department of Revenue article cited http://www.oregon.gov/DOR/PTD/IC_303_670.shtml, check out this page on the Multnomah County Tax Office's site: http://www2.co.multnomah.or.us/Public/EntryPoint?&ct=3e0 It's a very short, clear explanation of why taxes are what they are in Oregon.
If you'd like a little more detail, I have an article on property taxes in Oregon on my website: http://edburnham.mywindermere.com/index.cfm?fuseAction=conte