It looks as though the Kindle Fire has been, thus far, a huge success in terms of unit sales.
It seems that Kindle Fire sales may have fallen off dramatically after the Christmas quarter - and not just by an amount we'd expect for the post-holiday quarter. IDC suggests that sales dropped from almost 5 million units in the fourth quarter of 2011 to less than a million units in the first quarter of 2012. Amazon, like some other tablet manufacturers, doesn't report unit sales (it's not required to, but I think it should for the sake of investors - that's a pretty important metric when evaluating the future earning potential of the company), so we can't be sure how accurate IDC's numbers are. But they align with other reports that I've read (e.g. with regard to customer satisfaction) and help explain the better than expected earnings that Amazon reported for the first quarter of 2012 (fewer unit sales means greater earnings since they lose money on those device sales).
Anyway, I'm surprised that interest in the Fire has fallen off as quickly as it seems to have. I could point to a number of possible reasons, but the quality of the device itself may be the main one. For $200, I still think it's a nifty device - for a reasonable price it allows you to do a number of basic things that a lot of people want to do, even if the user experience isn't high quality and smooth. And in the context of content purchased from Amazon, it's pretty convenient - the integration is good. But the quality of the device is lacking a bit. I guess we'll see what Amazon does with the next (assumed) update of the device - will it stick with much the same kind of device or try to upgrade it for a better, and fuller, user experience.