I had a kobo that I used for normal ebook reading. I triked throwing some PDF's through it. It was more hit then miss and even on ones that it handled ok it was still barely usable. The screen was to small, the text flow was to slow page turning was to slow and on the kobo (shouldn't be a problem for the Kindle or Nook) you couldn't do any searches. So really the experience for using it as a gaming device was fail - but for book reading just fine.
Now that being said I now have an iPad. It's sublime for reading gaming pdf's on. Screen looks awesome renders them very well, it's fast, search-able and the screen size is perfect. For game book applications it's the shiznit. The experience is so much better then trying to read them on my laptop, computer and certainly any netbook that I've seen - though I imagine a tablet style net book would be pretty good.
Now the down side is that the iPad is around $600, I was lucky enough to win one so for me the situation is blissful.