[84LX89GT]

I go to Pacific raceways in Kent quite often now that it's racing season. if you're interested in clubs search a search engine for Mustangs Northwest, they have quite a few meets and they race other car clubs as well. I've heard it's a fun club. Bremerton raceway apparently is another good place to find mustang racers. Even if you just hang out and watch you'll find guys that are cool and like mustangs at any drag race track. I've talked to probably 5 or so mustang guys while racing and they're more than happy to talk (at least so far).
I don't know of any specific mustang "hangouts" though, there is a yearly mustang roundup at Bellevue community college that i've heard good things about but i think that it happened a couple of weeks ago or something.