J.C.
great question. I hope that no one takes offense by my answer...this is purely my opinion based on my experience!
I am from the northern suburbs of Milwaukee, spent a ton of time in the Chicago suburbs growing up, and my best friend in the Seattle area is from the chi suburbs. There are actually a good number of people out here that I have met from HP, Skokie, Glencoe, etc. We live in a neighborhood on the border of Bellevue and Issaquah (it is actually where those who live in a great neighborhood of bellevue have their kids in school because thee issaquah school district leaks over the bellevue border just a little bit in an area called Lakemont. I think Mercer Island is more stepford like than Bellevue. A lot of Bellevue areas are actually much older and not all that nice...for living...we chose Issaquah because of this.
Meeting people is a whole other story. I have been here for 5 years - I think that Seattle/East Side is a really FRIENDLY place, but relationships with natives rarely go beyond the friendliness...it's known as the "Seattle Freeze". The good news is that there are a lot of transplants...so while the majority of my close friends are not natives, I have a few who are, there is not a lack of friends, but being friends with natives is not always the easiest.
Hope this helps...I think that you would love the life out here - it is beautiful, good schools.lots to do and see (much more outdoors stuff than the midwest).
For the record, I have a 6 year old and a 3 year old...happy to private message more if you would like more of my opinion!!!