Hmm, i usually spend about £ 50-60 a month on books, mostly Pbooks, but over the last few months its been half of that, as I've been putting money away for my cybook.
Once I get it, it will probably be more e-books as I will have a somthing to read it on.
I do however find that for a lot of books I like to read, the E-book price is more expensive then the actual printed book, once you get the discounts, so will have to see.