I sometimes get a bit embarrassed that I make decisions based on book length. I think the reality is now that so many books are competing for my time that I try to allow the most chance for completing most of those books.
And although I won't necessarily dodge a big book (I have Anathem and Wise Man's Fear coming up before the end of the year), I will consider how I distribute them in my reading list. So for the reading club, which often brings up books that are not in my immediate reading plans, I will be more likely to balk at the bigger books. I also ditched Anna Karenina for one of the book clubs for a similar reason even though I would definitely like to read Tolstoy at some stage.