Powell's City of Books at 10th & Burnside NW is a must, though sometimes out-of-towners end up with the problem of how to get all those books they bought home.
I would go enjoy the different neighborhoods and their establishments (no shortage of great bars and restaurants here), if I were you. Alberta St., Mississippi Ave, SE Hawthorne, SE Clinton. NW 23rd is not bad for a visit. Other people can stick up for their favorite neighborhoods.
I really like Zilla Sake House on Alberta St. for their sake and sushi. My two bits on the sushi issue.
There are lots of great music venues. Check http://portlandmercury.com
for listings. That's a good resource in general.
You can get pretty much anywhere by bus:http://www.trimet.org
has a good transit trip planner.
Or friend up some of the RCR skaters. They're always going fun places and doing swell stuff.
I hope you have a good time.
Oh, one other thing you might do, which is sometimes fun, is go on up to the 30th floor of the US Bank Tower (SW fifth & Burnside) and have a beverage at the Portland City Grill. If it's a clear day, the view will be spectacular.
p.s. - Absolutely agree with Mean that you should get somebody to take you out to the Columbia Gorge for a hike or two.
Also, there's a ton of antiquing to be done in the Sellwood neighborhood, which is not far from Oaks Park, where most of the skating action happens. While you're in Sellwood, you can stop into Kay's bar for a beverage and some poutine.