IE9 is supposed to support all this, I think. Let the people that don't want to update live in their "square" world...it doesn't seem like they care anyway.
Unfortunately, my experience over the years has brought me to the conslusion that this assumption is incorrect. If an IE user comes to your site and it doesn't look pretty, they're less likely to switch browsers than they are to just go to your competitor's pretty site instead. It sucks, but that's the reality, and that's why almost nobody gives IE a totally degraded experience.
Instead, web developers use all sorts of tricks of the trade (sliding doors, complex overlapping sprites, empty divs positioned to corners, etc.) to "fake" the features that CSS3 gives us natively, solely because they are forced to support IE. That's what PIE was created to change. It's not about giving IE users a better experience (most sites already do a pretty good job of that already), it's about making the web developer's life easier so they can deliver that same experience with less code and fewer images.
And for most markets, that's IE, and frequently not even IE8.
But again...we're talking about adding overhead to a site JUST for eye candy. Let the boxes be square for IE...is that detrimental to your site's message?
But correct me if I'm wrong, like I said I'm just assuming.
If you are in a situation where you can simply forget about what your site looks like in IE, then I envy you. Most web designers are not.
lojjic, you should illustrate that in the docs somewhere.
behavior: url(path/to/PIE.htc);
that non-IE browsers will simply ignore.