I do the giftcard budget as well, and I've only had my Kindle for a month and change. It is very effective, and in fact has kept me from PURCHASING any book but one collection of books that was quite cheap. Everything else has been free so far. (; Knowing that I have that limited amount on the giftcard has been super effective for me.
Of course, I'm a major cheapo kind of person in the non-digital world, as well. So I guess it makes sense for that to translate over to the eBooks.
I also started looking around for ways to get free Amazon giftcards, like Swagbucks and a couple other sites. I gotta say I only have enough time/energy/drive to keep up with Swagbucks, though. I envy the people who can be disciplined enough to use multiple venues for giftcard earning. On another note, there are constantly new raffles and contests for giftcards that most people can enter, so I'd look into that if money is tight.
Plus, I ask for Amazon giftcards for my birthday and Christmas. ;D I hardly ever spend my own money on books that way.
The dark side is attractive, young padawan, but careful you should be.