I have a Kindle (bought 1 when it first came out, gave a 2 as a gift, now DX); plus kindle app on an ipod touch and on mac. iPad is enroute. Eagerly awaiting an Android app.

I have about ~150 books paid for (maybe more? I see 10 pages with 15 items per page). 1-2 books per week are consumed, but I tend to buy 5-10 at a time.