Quark hates our freedoms. I was having hell with Illustratior .eps files just yesterday. It gave me an error message when tried to display full resolution, then when I clicked okay, the size of the image changed on screen. (it became twice as big, but still looked low res.)
I was also having problems with the PSD import xtension, so I did a lot of tinkering, restarting, etc. I wish I knew what exactly made the problem go away. When I was able to get them to show at full res, moving them around was horribly slow. (dual 1.0 G4 1.5 gb RAM) Tap arrow key, wait 1-2 secs, img moves.
(psd import chokes on anything over 300 dpi, btw. and rather than saying "image too big" or something pertinent, you get an "invalid file type" message.)