I would say they look pretty good. It splits the page in half horizontally if it can. Actually, that's the cool part, it splits as near to half as it can without splitting through anything, so it never cuts lines or pictures in half, really neat actually, have an example azw/source pdf file of this if anyone's interested.
Anyway, once it's split, it displays it rotated 90 degrees to the left on the screen, so it's kinda like viewing a PDF on the sony reader rotated. I find the text large enough for me to read (though not by much) and the images overall quite crisp. The only thing I would be wary of is that the resolution of the source pdf needs to be as high and as sharp as possible, if it's overly smoothed or low res (anything under 100dpi) it really ceases to be readable. That said, I have now read about 30 pages of formatted scientific papers this way, and I think it works great.
For image PDFs of things like manga or comics I think it might be a different story though... since the system seems unwilling to split though a non-blank part of a page, which is pretty cool, it might just leave the whole page alone, which would make it too compressed to read reasonably given the resolution of the screen. Which brings me to the two big gripes with this method, no zoom and pan, and no text so no rerendering just progressive quality loss.
So you can see for yourself here's a photo of a particularly complicated piece of a scientific paper I was reading the other day rendered on the kindle.
http://people.cs.vt.edu/~njustn/DSC00355.JPG