Here's my trip report:

I set out in the rain, which would have been fine if my Gore-Tex boots and DWR rain shell had actually been waterproof, but seeing as how they let in plenty of water and made me freeze my tuchus off and accelerated the blisters, I had to cut my first day short and set up camp early so as not to get the hypothermia. This also cut short my second day because the park and its air were too moist and soggy to allow for any drying, so I went for day hikes around the neighborhood, which was very nice. Henry Coe's hills are no joke, as there's no switchbacks, so you'll cover the same uphill in 2.5 miles that would normally take 3.5 miles with switchbacks, and be more tired!

Even with the rain there's still not much water in there. I camped next to a creekbed that had only puddles, half-frozen over. There are plenty of crusty old cattle ponds that will make you very glad you lugged your 1-lb filter along. The scenery is beautiful, the park is vast, the views are great, the wildlife is plentiful, and the solitude is hard to imagine so close to the Bay Area. You'll have to come next time!