[Note: The following is a summary of a "10 Questions" feature produced by Sulthon of Kingslanding.org, which is now defunct.]
Martin does a lot of research on any story that has a historical or quasi-historical setting. For the series, he immersed himself in the Middle Ages, reading everything he could about such things as castles, tourneys, knighthood, food, medicine, clothing, and customs. He also read histories of things like the Hundred Years War, the Wars of the Roses, the Crusades, and so on. In his opinion, the more you can take in of a period, the more your work will have a sense of truthfulness.
If any sort of accident would bring about an early end for our favorite author, such as a meteor flatting his home, the readers will be flattened with him. There is no "master outline" for the series, just a half-dozen pages of very rough notes that are largely out of date. If he should die unexpectedly, the publishers might hire someone to finish the series, but they'll be on their own and will be very unlikely to finish it the same he would. However, he's only 52 years old, and had had a full physical in February, so he doesn't think there'll be a problem.
We'll learn what "valar dohaeris" means in A Dance with Dragons
Tyrion is Martin's favorite character, but from the perspective of House Stark, he's certainly a villain -- someone once said that a villain was a hero on the other side.
At the time of the Sack, Aegon Targaryen was, "Still a babe at the breast. A year old, give or take a turn or two."
Martin had once stated that Gandalf should have stayed dead (in Tolkien's The Lord of the Rings). He still holds to that position, despite some of the events in A Storm of Swords. However, if "he had returned as an evil flesh-eating zombie", that could have been different. Martin does not believe his "resurrections" are remotely similar to what Tolkien did. Death actually made Gandalf greater, improving him and increasing his power. And, quibbles aside, Martin still thinks that Tolkien was the greatest of all fantasists.
Martin has no central resource for his knowledge of the Wars of the Roses, but he has a bookshelf packed with related materials. Special mention goes to Thomas B. Costain's 4-volume history of the Plantagents, however. Though the wars are dealt with only in the final volume, the books are extremely readable and full of colorful anecdotes about the times and the people who lived in them.
Martin says that all young writers go through an imitative phase, and that it's not a problem. It can be a useful learning experience, and eventually one will find one's own voice.
Martin recommends Tolkien's The Lord of the Rings, Robert E. Howard's Conan and Kull stories, the Gormenghast trilogy by Mervyn Peake, Peter S. Beagle's The Last Unicorn and A Fine and Private Place, Fritz Leiber's stories of Fafhrd and the Grey Mouser, C.L. Moore's Jirel of Joiry stories, and Jack Vance's Lyonesse, The Dying Earth, and Cugel's Saga. He also recommends historical writers such as Sharon Kay Penman, Nigel Tranter, Cecilia Holland, Thomas B. Costain, and Maurice Droun.
Martin likes all sorts of food. Living in Santa Fe, he's a bit of a snob about Mexican food, however. New Mexico has the best Mexican food in the world, much better than Sonoran or TexMex, so he never eats Mexican food away from home. He loves Chinese food as well, especially Hunan and Szechuan styles that are extra spicey. Greek food and pizza as well, but only the thin-crust New York style pizza.