TechCrunch is reporting that according to their sources, Amazon has shipped 240,000 Kindles since launch, suggesting a $100M business so far:
Doing a little back of the envelope math, that brings total sales of the device so far to between $86 million and $96 million (the price of the device was reduced to $360 from $400 last May). Then add the amounts spent on digital books, newspapers, and blogs purchased to read on the device, and you get a business that has easily brought in above $100 million so far. (Each $25 worth of digital reading material purchased per Kindle, add $6 million in total revenues).