Horrible. The screen refresh was fast enough, but the actual PDF rendering was grossly underpowered. I was reading technical articles with embedded plots that would take quite literally minutes to render.

I sold my DX (the "current" gen) and bought a 3rd Gen iPad the minute the retina display was released. I still pine for the eInk display though. I've half considered a hobby hack project that involves a Kindle DX brain transplant.