i think overall i'm a fairly fast reader but there are some books i read very slowly. maybe because the prose is so gorgeous i want to savour every word (Alessandro Baricco comes to mind...) or because there is a lot of information to take in (nonfiction) and sometimes if the characters' names are too similar or if there are a lot of them i get them confused (i'm terrible with names, including in books) and i have to keep going back to remind myself who is who...
luckily the 700 and the eb1150 both allow me to turn pages quickly so i can easily go back a page or two when necessary.
i also sometimes skim the previous page quickly when i pick up a book again to remind myself where i was when i stopped, particularly since i like to read two books (or more) at the same time.
i'm (re)reading moby dick on my telephone in the métro right now (using a bookapp from booksinmyphone.com) and it's a bit frustrating for that because there seems to be some strange bug where if i try to go back one page it sends me back to the beginning of the book, so i can't do that. i'm pretty close to switching that book over to my 700 instead because there are often passages i'd like to re-read just because i enjoyed them so much (moby dick is a really funny book, and very well-written) and also to take advantage of the highlighting / note-taking features to mark the passages i particularly enjoy and come back to them for future reference. that's another thing that makes me read more slowly.