When I put a figure into my document (doesn't have to be bitmap, PS does the trick as well, I think the distinction is color vs no color), the on-screen resolution of the text changes at the default level I'm viewing it. Basically the effect is that as soon a figure is included, the quality of the PDF seems to get worse. If I zoom in a bit, it gets better, but I'd of course like my PDFs to look properly in full-page mode as well... I don't know what setting this might be - maybe someone knows the phenomenon.
Edit: The two screenshots below show the phenomenon with differents levels of zoom. The left is the "broken" one. The right one is how things look like when no figure is "near".
Edit 2: Interestingly, I get back the right preview from the broken one if I print the left document into a new pdf via CutePDF. This is not a real solution (file size gets blown up for other reasons) but shows that information isn't really lost, just somehow weirdly displayed as it seems.