If you use your iPad to read books from Amazon (Kindle), it appears there is a problem with the most recent update to the app (see the date of this post as the problem is likely to be corrected soon). You should at least read this warning from TechChrunch.
Concerns are expressed by users in comment posts to the iPad app page.
Could be a hoax, but you may also want to wait before updating. You do not actually lose the material you have purchased as it is stored by Amazon. I also do not see the value in keeping a huge collection of what I own on my device, but some take this approach.