Oh my gosh - I was going to post the same thing!! YES - I'm in California too and had this EXACT problem with my roadster. I've never owned a convertible before, but I found it hard to believe that it would be like this in other cars.

I disagree it's due to having a collection of water on the roof - this would happen even after having just been driven and parked, with no visible water collected. Just open the door - and in comes the water. After the second day I started to carry a small towel in the car to wipe it up before sitting in it or leaving it there when walking away from the car. What a bummer though for sure. Very dissapointing.