While I prefer new whenever possible, my funds require I by used most of the time. Especially with books, I've got tons of used books for a penny each, as opposed to Ł7 for new ones.
With video games I'm more wary, as I bought several used games that turned out to be fakes, so I only go used for old GC & GBA games.
I also got a PSP used in good condition that worked fine for years, but the disk drive broke so now I can't play anything but FF Tactics on it...