Are you talking about SF to Portland . . . Or SF to Portland, and back again?

Makes a BIG difference both re route(s) and how much you can see/do.

I was thinking to fly into San Francisco and fly out from portland

That helps a lot.

You will have enough time to see quite a lot - but not everything since both are very big states w/ a LOT to see/do. Not having to backtrack will definitely help.

Are you interested in Napa/Sonoma wine country at all?
How long do you want actually IN San Francisco?

w/ 10 days and at least a couple of days in SF, you could do something like:

SF 2 nights, Sonoma area 1 or 2 nights (totally optional depending on the 'wine interest'), Mendocino/Ft Brag area 1 or 2 nights, somewhere in the Redwoods in far northern CA 1 night (lots of options), SW Oregon coast 1 night - a couple of options for your route from the coast over to Portland 1 night, and ending up w/ a night or two in Portland.

7 days would be harder w/ more compromises but a reasonable itinerary could be worked out

W/o the wine country stop you'd have time to add something like Crater Lake in Oregon.

I would go up the California Coast (this includes Napa/Sonoma) and then go inland to see the Oregon Cascades (Crater Lake) and maybe some of the high desert country near Bend as you weave around Oregon (basically there is the ocean and coast and the Cascades)

http://www.flickr.com/photos/mksfca/sets/72157631954074484/show/

http://www.flickr.com/photos/mksfca/sets/72157622981132189/show/

With 10 days you could fly to SFO (or Oakland) and go to Napa/Sonoma. From there head north on I-5 to Medford Oregon or Crater Lake Lodge if you can get a reservation. When you leave Crater Lake, head for either Bend or Portland.
When you leave Portland, head to Astoria and then south on US 101. There are many great places to stay along the Oregon Coast. You can make the entire loop within 10 days and fly home from the airport you flew to to avoid a car drop off fee.
This loop would also work if you flew to Portland first.

Like theatre?

http://www.osfashland.org/

http://www.ashlandchamber.com/Splash.asp

I personally would not do a loop. That is a LOT of territory/mileage/rushing just to save a possible drop off fee.

Whatever else you do, I suggest you include the Redwoods in northern California, Highway 101 from Eureka to Cannon Beach, and the Columbia River Gorge.

Our favorite towns to stay along Highway 101 include Garberville, in California, and Brookings, Bandon, Yachats, Newport, and Cannon Beach in Oregon.

In the Columbia River Gorge, we like to stay in Hood River.

HTtY