I've had my Castelli Pocket Liner Jacket for a couple of weeks now, and I'm thrilled with it. The waterproofing really is as good as everyone says. While it's not perfect - I got caught in a surprise hard storm yesterday and I did get somewhat wet through the jacket - I've stayed dry through rain that would have soaked me in my Gore Phantom soft shell.
One key feature that not too many other people are talking about is its windproofing. I think its windproofing may be better than its waterproofing. I've ridden in mid-40s (Fahrenheit) with just a short-sleeve jersey on under the Pocket Liner Jacket and I've been completely comfortable. This is a fantastic solution for bike commuting in the Pacific Northwest: wear your jacket over your jersey for your 45 degree ride in; fold up your jacket and stuff it in your jersey for your 85 degree ride home; or wear it both ways if it's raining.
As a quick note on sizing, the Pocket Liner Jacket runs very large (for Castelli anyway). For reference, I usually wear Large in Gore, which translates to XXL in Castelli. However, I got my Pocket Liner Jacket in XL and it's slightly big, definitely not a "race fit". This is not criticism, just something to be aware of. I do wish the rain flap in the back were a little longer, but this is a very minor criticism.
Again, it's a great jacket and a great purchase. Highly recommended!