As far as parts of town -- I've mostly poked around downtown/northwest/pearl district, on the west side of the river where transit's really good. Been to a few restaurants on the other side of the river, and of course the convention center is on the east side but there's nothing fun near it. ;)

I remember the first time I visited Portland (for OSCON I think, some years back) I was struck by how *clean* it was compared to San Francisco... Wide streets good for cars but still very walk- and bike-friendly, and I really like the light rail. (Unfortunately they no longer have a free transit zone downtown, they started charging a couple years ago to make up budget shortfalls.)