LOL ... I purchased my first ebook before my Kindle arrived and started reading it on my PC. I had just finished the last book in a current series and the next one was debuting the following day. I was so hooked into it I had to purchase it immediately! Couldn't wait the 2 days it would take for my Kindle to arrive
But now I'm faced with a similar dilemma. For the most part though I follow the same criteria. While I have downloaded many of the classics, my purchases are mostly for books I haven't read yet. The one exception was when I was FINALLY able to find some Heinlein in ebook format!