I did this survey back in 2007. A lot of my D&D 3.x gaming books had errata and FAQ documents compiled by the publisher to help clarify and correct oversights in the printing. I had embarked on a quest to make sure I know what needs to be corrected, so I bought a bunch of transparent 1/4" sticky dots.
If an errata indicated something is to be deleted, I placed a red dot over the beginning of the text to be excised. If something was added, or improved on by the errata, I used a green dot. If something was otherwise changed or required reference, I used a yellow or blue dot, depending on the tone or which color would show up better.
I had refrained from actually writing in corrections, or making any other notes on the pages of the book. However, once I finished with my D&D books, I promptly stopped doing this altogether.
I'm curious how other gamers deal with errata, so I compiled this poll. Please let me know what you use to deal with this phenomenon: