I used free knitting patterns from the interwebs to test with.
PDF #1 Source:
http://www.saartjeknits.nl/ (right side of page)
It has seriously issues, none of the text was rendered.. I heard from a comment on a blog that if you create a word doc and export as a PDF then convert on kindle it can have these issues, I can't substantiate that though.
PDF #2 Source:
http://www.helloyarn.com/wp/?p=370
Totally perfect conversion, even the image is in the perfect shape/size.
So I suppose it just depends on the PDF etc... I've been disappointed so far in that some HTML i sent through came through the kindle with a html P tag visible on every paragraph and then a .txt file I sent through (my address book, really simple text) came through with wacked out formatting, and even the Atlanta Journal Constitution (Newspaper) which I subscribed to has these weird "?" icons in it at certain places.
So far I am seriously un-impressed by the conversion Amazon does, or at-least the lack of consistency, however with that one perfect PDF conversion I know there is hope.