If I try using an alpha value in an RGBA color (rgba(0,0,0.0.5) for example) in a background gradient or box shadow, IE seems to render the solid color, ignoring the alpha value. Is this a known issue?

Yes, both issues are logged in the issue tracker. Unfortunately there are only a couple places PIE can currently render rgba alpha, and they're described on http://css3pie.com/documentation/suppor ... -features/ in the "rgba color values" section.