I have to say that for those of us in the UK or Europe, The economies often work out better, if we're willing to buy from US Based stores.
Being a student, I have a Hard Limit on my Budget as to how much I'm willing to and able to spend on Books. (Also Being a Gadget Geek, I need to put away money for that as well).
Anyway I usually budget between £50-70 ($75-110) a month. Books here in the UK tend to be Expensive, with Paperbacks starting at £6+ and Hardbacks around £15-20.
While there are discounts, it does pile up.
Buying eBooks has been a boon in that. I can usually buy eBooks at 50% to 60% of the paper price and in many cases even cheaper.
Just an example I Bought
Nation By Terry Pratchett from Fictionwise for $11.86 which is about £6.7. The book is only out in Hardback right now, with a list price of £15 and average discounted price of £10-12. I Also got a Micropay rebate of $6 so It actually only ended up costing me about $6.
While I will probably be buying this particular book when the Hardback goes further down in price, for the majority of books, I don't need or want a physical book, especially in the case of Thick and Heavy books like Bill Bryson's Short History of Nearly Everything.
For Such books, the convenience of eBook's is hard to beat. Also, when ravelling, its really nice to eba ble to carry a large library with me, without having worry about whether I have enough space, or will I be able to buy the book's I want where I'm going. (try finding a decent selection of English Language books in Lebanon or Egypt, its not easy)