I commute through Seattle from the ferry dock to south lake union. I could technically do it in two turns, but that wouldn't be great in terms of avoiding hills, avoiding streets with heavy traffic (i rode on denny during commute once, not going to happen again), and avoiding the damn trolley rails (also, not going to touch westlake where the trolley is again either).
I don't choose to ride on 2nd ave, because it's too different for the one or two blocks I could be on it, and the transitions are hard. It's a much better idea than some of the other protected lanes I see on my route though. I can't imagine it's worth it for me to go up and down Marion to use it though. (Western is a much nicer slope)
Inside a city these dedicated bike lanes are great, especially with dedicated bike traffic lights. Obviously doesn't apply to longer/winding rides.
I'm in Seattle and we have one here (2nd Avenue) that "feels" a lot safer than cycling alongside parked cars/traffic.