I'd estimate ma throughput at about 20-30 a year. Most of those have a lot of pages so it takes me about 2 weeks of "spare-time-reading" to get through them. I I read paper or STAReBOOK I'm a lot faster than when I read Iliad, but I've come to love the ease-of-use of the mobipocket format on the Iliad so I tend to go with the Iliad again now most of the time and take the disadvantages as acceptable if annoying side-effects.
If it' a really good year with lots of good new books, then my book consumption goes up of course...