So far she's only gotten two answers from fellow Questionlanders, but CleverScreenName has some mushroom-worthy advice:
You've already got an excellent resource at your fingertips: the newspapers. Read the loctal news and get a sense from The Stranger about what's going on around town and where things happen (use a map if need be). The Seattle PI also does a kind of overview of the neighborhoods and haa neighborhood blogs. Some of blog content is BS, but it can help you get an idea of the neighborhoods at the micro level. Newspaper articles will help at the macro level.
Once you get here, pick an area that your reading has made you curious about and start exploring on foot. That's the quickest way I've found to get up to speed on a new city. You'll be able to linger, see the kinds of posters that are up in businesses, see what the people around you act like, and even appreciate how much vegetation is around you and how it affects air quality. You can't do that in a car.
One final thought: you can make Seattle pretty much what you want it to be. My friends experience the city in a wide variety of ways. If one aspect of the culture doesn't do it for you, chase another and see what you find.
CleverScreenName's answer has been awarded Answer of the Week so both CleverScreenName and Arianna have won a $25 gift card to Pagliacci Pizza! It will no doubt come in handy while exploring Seattle.
The pizza may have been won this week, but it's not too late to help Arianna out—if you have tips for a new city dweller, head over to Questionland!