I'm using the border-radius and box-shadow properties on about 30+ elements on a single page.
Everything renders fine in IE6-8. The trouble begins when I run an animation that opens a child element using an expanding/contracting animation (the native jQuery slideDown() and slideUp() functions). In IE8, the animation is extremely choppy. Strangely enough, IE7 and even IE6 seem to have little trouble - the animation is very smooth!

Anyone have an idea why this is happening and how I can try to address it? As a last resort, I might just use that meta tag to force IE8 to use the "IE7 compatible mode", but I'd like to first see if there isn't some other solution.

Oh, and I did try using the -pie-lazy-init property which seemed to help somewhat, but IE8 was still much too slow.

I can confirm that IE8 is much slower than 6 and 7 at animating. I do not know why that is the case. The slowness is even evident when only moving an element (not changing size or other properties, just the top/left), which runs very little of PIE's logic, so it seems to point to an inherent inefficiency within IE8's engine.

Sorry I don't have a better answer for you on that.

Hmmm, well at least it's good to know that I'm not the only one with this issue
Looks like I'll have to resort to forcing IE7 compatibility mode.

One common that makes animations of IE8 slow is the transparency of images that repet themselfs when used as css background.

So if you have one little image with transparency that gets repeted as background it makes ie8 slower; try to change it to a large image with no repetition (no-repeat).