It varies, but generally whenever I have free time and don't feel like gaming. Or, when playing a slow game like X3, while gaming. I probably average a book and a half a week, but since they vary in length so much it's hard to get a reasonable estimate. For example, I recently read Great North Road (awesome), which is over 1100 pages long and took me about a week to read, but then I read The Departure which is much shorter, which took me half a week, even though I didn't read it so often because it wasn't as good.