An LTE tower lit up in the South Lake Union area:
http://www.sensorly.com/map/4G/US/USA/Sprint/lte_310sprint#q=98109
Speeds have been... less than encouraging, though. The best I've been able to muster so far was about 3.6Mbit up, 2.1 Mbit down. The speeds jump around a lot, the signal is a bit weak, and most speed tests are well under 1Mbit to Seattle servers which can easily do 100Mbit+ speed tests. Bandwidth isn't everything, and the latency is generally good - about 60-90ms - but it's really not looking great for Seattle proper so far.