How important is it to visit during ASW as opposed to some other weekend?
I felt like ASW gave me a good sense of what Boalt was about. I think you should try to go if you can.
How do employers outside of CA look at the grading system?
I don't think that employers outside of California view the grading system any differently than the employers in California. Boalt has had a non-traditional grading system for decades, and Boalt grads work all over the country. If, however, you target small firms that don't come to OCI and that rarely interview Boalties, you might have to explain the grading system in an interview.
By the way, Boalties who target firms in NY and DC appear to do very well. If our grading system has created problems for those students, I haven't heard about it.
Is having straight Ps truly equivalent to being a median student at a peer school?
No. Employers will treat a student with straight P's as below median. The firms that participate in OCI seem to have a pretty good idea of what mix of H's and P's constitutes "median" at Boalt.
The main benefit of the HH/H/P system is that you don't have to worry about bombing an exam and having a B- on your transcript. The main drawback, of course, is that you can score above median and yet still have the same grade as someone who finished near the bottom of the class. I think it generally evens out over the course of a year, but—as with any grading system—some students will get lucky and some will get unlucky.