@ Phil the Geek re: Protx
Protx isn't bad; I pay through it when I buy nipple rings from Wildcat. However, there are elements to its design that fall short of "fully baked."
In particular, it depends on cookies but nowhere does it say so, and if you have cookies disabled by default like a sensible person, you don't get an error of any sort. Or maybe the error is a pop-up blocked by Firefox because it uses spam/scam popup techniques.
Moreover, Protx sets cookies not only for itself, but for a domain named something like "securepayments.net". (I don't have the cookies on file any more, and don't remember the exact domain name.)
I'd say the problems with Protx, while not serious, are due to a lack of transparency. All they have to do is lard their pages with "here's what we're doing and why and how you can adjust your browser settings to make it all work."
To the Protx people reading: try it out on Firefox 3 with cookies disabled by default, popups blocked, and AdBlockPlus operating. You'll see what I mean.
In a way, it's a textbook case of what happens when you assume everyone is an idiot using IE with unaltered defaults.