As a person also in the process of relocating here are my thoughts, feel free to discount them based on your own experiences --
Pros: Mariners/Seahawks! Pyramid Brewery! Arts/culture! Museums!
Cons: Washington is a lot like Pennsylvania - the one big city is awesome, but the rest of the state is basically Southern shotgun wielding rednecks. Also not a ton of "successful young single people" it seems more like an age 30-40s married couple haven from people too boring to raise their kids in LA or San Francisco. Also UW students are more obnoxious than Ivy League kids - congrats on accomplishing the impossible children!
Pros: Outdoorsy. College town. Reed students are really nice, good dating material. Lots of fun restaurants. The river! The nature just outside the city like Mount Hood! People are super-friendly, like in the stop-and-ask-for-directions way.
Cons: The biggest building downtown is Kaiser Permanente. The downtown area is sort of small. The town is sort of small. Not a skyscraper city. It seems like a place you can "grow out of" within a very short time, especially if you are ambitious and more oriented to "big city living" like LA, NYC, or London.
Pros: La Jolla. Mr. Taco. Coronado.
Cons: Everything else.
Cons: mucho minus one
Since that is where I have probably chosen to relocate I want to hear what others have to say about it first