Hey,
I'm new to diving and I have to say that PADI's website rocks. Found what I needed, found a dive shop quickly and even signed up for the open water diver course in a few clicks.
The site was fast (I think they resolved the issues that you speak of) and I was using a MAC and Firefox and everything worked fine for me.
In comparison, I tried SSI's and SDI's and they both sucked. I had problems finding a shop with the dive shop finder thing, it sucked in comparison.
I was also happy with the online course work from PADI (and I'm a teacher). Job well done. I have no complaints and have recomended three of my friends already and they have made to same positive comments