On a forum I follow, someone posted the ranking of large metros by urban density based on recently released ACS data. Portland was #10. Top 10 are as follows:

1. SF @ 7,626 ppsm
2. LA @ 7,476 ppsm
3. SJ @ 6,436 ppsm
4. NYC @ 5,981 ppsm
5. Vegas @ 5,046 ppsm
6. Miami @ 4,885
7. San Diego @ 4,550
8. Denver @ 4,168
9. Sacramento @ 4,163
10. Portland @ 4,052