I've been collecting comic books for about four years now.
During these years, I've spent a lot of money. For the first two years, my whole collection (Except one hardcover and one trade) was comprised of single issues.
I don't know what happened, maybe Genesis took over (Ha! It's a comic book joke in a comic book forum! That makes it funny!) but suddenly, I started buying more and more trades and hardcovers (And sell some, in order to buy more).
I still buy quite a few issues per month, but my graphic novel collection, which was comprised of two books only two years ago, now contains about sixty (A little less, I assume, as I sell a lot).