The train is much slower than driving and notoriously unreliable.

You can drive downtown to downtown in under three hours. The flight time is about 45 minutes, with block-to-block time usually about an hour, but total downtown-to-downtown transit takes about 2.5 hours. The five daily Amtrak trips are timetabled at 3.5 hours to more than four hours, depending on stops.

I usually drive.

With all the business travelers shuttling between Seattle and Portland and fuel prices going up again, I think this would be an excellent route for some kind of express highway parlor car operation... sort of like the Hampton Jitney... with big comfy seats or workstations and lower-than-Amtrak fares. I think there's a pretty interesting business proposition in there.