Nope, we are not. I checked it out but mostly decided that it didn't provide enough difference for the cost for us. We haven't 100% made the decision but we will have to in a few weeks.

I am interested to see what others say.

We built in the Pacific Northwest (3 hours north of you) and stuck with basic fiberglass due mainly to cost. Instead, I would suggest investing in good windows and doors, properly installed. I've got some defective single hungs that are driving me nuts with the amount of leakage coming through. Good thing for lifetime warranty.

We are in North Snohomish county - used fiberglass, also due to cost. We used good doors and double pane windows. Ken Root Insulation (Arlington, I think) and TLC Windows (Arlington/Smokey Point) if you want some recommendations. Both were excellent; Ken sent his guys out on a Saturday so that we could meet our building schedule. Good for him!

Why the interest in spray foam? Much cheaper options particularly for a mild climate with low energy costs and carbon intensity.

I'd suspect a well built house with good air sealing in Seattle area would be very cheap to heat with just fiberglass. The spray foam payback might be more than a lifetime. And if the concern is energy use, it might take several decades to reclaim the embodied energy in spray foam vs fiberglass. And then if you account for the aerosol effect on the environment, it is hard to justify by any means using spray foam in Seattle.

Not financial, not carbon, not energy, not environment. So if not any of those reasons, why spray foam?