When I was trying to recommend Mistborn to a friend who liked fantasy with good worldbuilding, I skipped over all of the cool, non-spoiler-ey parts like the ash and the magic system and jumped straight into babbling about Hemalurgy and Shards. I think I spoiled decent chunks of all three books in the Original Trilogy before I realized what I was doing. At least I managed to keep my mouth shut on all of the kandra-related spoilers, despite TenSoon being my favorite character. Also, with this same friend, when I was explaining the cool question I had come up with, I completely forgot that Feruchemy was kept intentionally mysterious for large portions of the first book, and I think she is smart enough to be able to guess several important plot points from the background I gave her on it.
Speaking of Mistborn spoilers, since I have no self control with TV Tropes's spoiler-covering system, I managed to spoil practically every single plot point of the original Mistborn trilogy before I had even finished the first book.
The first time I read Way of Kings, I listened to it on audiobook and was only able to get about halfway through before I gave up/had to return it to the library. I think there might be something about me and audiobooks not working well, since when I went back and read a paper copy, I finished it in like three days and managed to comprehend significantly more of it.
I once made myself late to my 9 AM class because I started a Writing Excuses episode I didn't have time for. Fifteen minutes long, because I'm in a hurry and apparently not that smart.