Seattle Transit Blog picked on this story some time ago, but Sound Transit has published their new June schedule book (4mb pdf).
There are a few schedule changes to the 574, 577/578, and the 590 series. Some trips have been eliminated from the 586, 590, 592 and 593. And the big new thing for Pierce County is the addition of Saturday service on the 578. The new 578 Saturday service will be hourly starting in Puyallup traveling through Sumner, Auburn and Federal Way and then going express to Seattle from 6am until 8pm. On the way back, it will be from 8am until 10pm. Since the 577 and the 578 will alternate this means that there will be half-hourly service between Seattle and Federal most of Saturday.