Thanks for the perspectives/discussion everyone. I had heard of the Zend certification, so I looked in to it and saw how pricy it is. Not sure if nothing but the PHP certificate would be very useful to me. Maybe I'd do it if I had a job possibility that specifically required it.
I took the W3 sample test and did pretty well (with no specific prep other than the past 10 years of messing around with this stuff)...but maybe that was sort of a "come on" and 70 (much harder) questions would appear after I paid W3 $95 for the real exam. Also, the business of finding your own proctor/witness for the W3 exam sounds kind of sketchy (Hey! I used a young person's word there.).