I've been working on somewhat unrelated IE polyfill work, and have come across a technique y'all might find interesting. I want to run it by the community first to get a sanity check before investing any time submitting patches for CSS3PIE.
(1) Have a second HTC file whose sole purpose is to scan the browser's stylesheets for unsupported properties or idioms. This behavior would be bound to body (for example).

(2) Rewrite the rules that use :hover to .pie_hover for IE6. Similar for :active. Bind mouseover events to the body as a delegate so that only one event handler must be bound (instead of per-element).

(3) Rewrite the rules that have "display:inline-block" to be "display:inline;zoom:1" for IE6/7.

(4) Rewrite the rules so that "opacity=x" are converted to "filter:alpha(opacity=x)" for IE6/7/8.

(5) Rewrite the color property (or -pie-color) so that rgba, hsl, and hsla values are supported. Obviously, discovering the background color would be needed for any alpha values.

(6) Add a -pie-ignore property so that individual polyfills can be skipped, e.g., box-shadow, opacity, etc.

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So far, this will have taken (a limited amount of time) for stylesheet/rule scans and other initialization, but no appreciable runtime cost except for opacity.

The next is where the greatest cost would come from.

(7) Add the standard CSS3PIE behavior to each appropriate element, so that you don't have to specify each and every rule to use CSS3PIE.

(8) Add form validation for HTML5 attributes such as @placeholder, @type=email, etc. via behavior.

Edit: Forgot one.

(9) Add support for position:fixed to IE6.

The goal? Make IE6/7/8 less of a separate code path in future projects and reducing the need for most of the common CSS preprocessors. I have most of these items working and have only recently noticed some of the overlap of my work with CSS3PIE, such as with hover events. What do you all think? Worth using or off my rocker?

Oh! Almost forgot.

The stylesheet scanning behavior would have to be a separate HTC file. This means that the functionality would be inherently optional. Either make the explicit CSS additions yourself or have it done automatically knowing that there may be a tradeoff in speed.

So I'm curious: do you get tired being right all the time?

Yeah, the scanning behavior only loaded after the body tag was fully loaded. Bah. Separate JS file it is.

@xem Nice but the main problem is about performance when using pie.js is not really important from my point of view how is applied And other problem to apply pie.js on elements when dom was modified
However your work looks fine