So I just created a fairly large PDF. The largest document inside of it is 1024 pixels wide. I just previewed it in slideshow mode using Preview and it's showing me two slides at once on my screen. This is happening on both a 27" iMac and an 11" Air. I don't seem to remember Preview ever doing this before. I also viewed the PDF in Acrobat and it displayed fine, one slide at a time. Has anyone ever experienced this, and is there something to turn off in Preview so it only displays one slide at a time? I'm using Lion, if that possibly accounts for it.