On Tuesday morning as I boarded the 545 to go to work I noticed a logo next to the door. Apparently, my bus had WiFi access.
In five trips since I noticed the logo, only once has there not been WiFi access (twice the bus hasn't had the logo, once it did have wireless, once it didn't.
Sound Transit has started a pilot project to provide WiFi on select express routes and on the Sounder. According to the web page about the pilot, the most common routes to find WiFi are the 545, 522, and 577.
I've got to say, it's a nice addition to the commute. I'm sure many of my fellow riders appreciate it too, given the number of laptops I often see open each ride!
Community Transit in Snohomish county has been offering the service since Autumn 2005 (see the press release here)