As a side note, I’m getting addicted to pdf books: I print
them (I hate reading on screen, but it’s great for
searching), so I can annotate them, highlight in
yellow/red/green, glue/tape schemas, etc… at will without
feeling guilty.
If you’re using MacOS X, Flysketch[1] will allow you to highlight text,
add doodles, scribble in notes, etc. to just about any file so you could
to the same with your PDF and ehm… save some trees. 