I know I'm pretty late to contribute to this thread, but here's for anyone considering on going to Seattle.
I live in the Seattle area for almost my entire life and I find it quite relaxing and the people seem laid back and easy going. Kind of like a small town feel in a major city and very democratic.
Yes, it rains quite often, but normally in the months of fall, winter, and early spring. Mostly it is more like light drizzle and gray overcast skies. I don't mind it at all, but some don't like it. Weather is cool and damp, it doesn't get to the point of freezing, and we don't get more than a few days of snow. The summer months are great, pretty mild but it can get too hot in mid July - August. Overall the weather is not that all bad as most make it out to be, but the warm sunny days and fresh clean air make it worth it.
For the outdoor enthusiast, this is the place. Puget Sound right at your doorstep, Lake Washington nearby, and mountain ranges east and west. There are three national parks (Olympic, Mt. Rainier, North Cascades) within hours of driving distance, and a few others as well. Lots of outdoor activities and places to go camping, hiking, biking, fishing, kayaking, whale watching, and so on.
Seattle does have a nice art, music, and multicultural scene. Nirvana, Soundgarten, Pearl Jam, and Mudhoney put Seattle on the music map, Jimi Hendrix was born here, and Bruce Lee is buried at Lakeview Cemetery in Capitol Hill. Pike Place Market, Pioneer Square, Seattle Center, and Broadway are some of the vibrant places in downtown.
The major businesses are based here: Microsoft, Boeing, Starbucks, Costco, Amazon.com, Real Networks, just to name a few. However the job market here wasn't that great for the last year or so, but it seems to be improving now. Housing and rent in the Seattle area is very expensive compared to the rest of Washington State, and typically a one bedroom apartment would set you back $400 - $ 1500 a month depending on location.
It has pretty much gotten crowded - and more expensive - over years, and people are moving in from all over because partly due to the city's hip and trendy atmosphere. The traffic during rush hour sucks, on-going road construction, and a lot of asshole drivers. However, there are many great windy roads and scenery outside the city you can drive on.
As for San Diego, I've been there three times visting relatives and the weather is pretty and warm nice year-round. The beaches and downtown are beautiful, but I tend to find other parts of the city and suburbs pretty boring due to the acres of housing development. Overall it's a nice city, but I don't think I'd want to live in SD, partly because of the people there. I don't know, but a lot families seem to have a lot money and even the high school kids drive newer BMWs and Mercedes.