Should I purchase Infinite Jest now or wait for the new edition?
You may as well get whatever edition’s available on shelves. For what it’s worth, I’ve read books that are ancestors of Infinite Jest (Gaddis’s The Recognitions; Pynchon’s Gravity’s Rainbow) multiple times each, but have only felt the need to read Infinite Jest once since I first got it (I have the first-state, first-edition hardcover, identifiable by the misspelling of William T. Vollmann’s name on the back cover: nyah, nyah, nyah). I’m not sure that a new edition would make a significant difference in the reading experience, though I do remember the book having a fair number of typos. If the quality of the book as a physical object is your greatest concern, Infinite Jest is still in print in hardcover in the United States. Amazon.com sells it–consider importing. The hardcover’s ever so slightly larger than the paperback, and the pagination’s the same (I believe). Given the size of the type for the footnotes and the bare-bones typesetting, the larger the book, the better.