> What is the actual likelihood that Amazon will delete books from my Kindles (I own 2)?
The odds they will suddenly delete your content? Probably low. But consider this: Every Plays for Sure track sold by Walmart, Yahoo! and Microsoft is now dead. Every Divx disc sold by Circuit City is deader than Circuit City.
The AZW format currently used by the Kindle will eventually be abandoned for ePub and someday Amazon will abandon support for the 'legacy' format in a future product line. Assuming they even continue making hardware long term in the first place. And when Amazon abandons AZW, just remember that it is illegal for anyone else to crack one open. Thee and me would know where to go to fix that, most folks won't.
And that is why investing in closed systems is usually a losing game. Unless you only care to use the content RIGHT NOW and couldn't care less that it has no future you should avoid DRM and other closed systems. So Netflix is ok, closed books aren't. I didn't buy a DVD until Mplayer gained support. No I didn't have a PC hooked to the TV at the time, but why buy into a sealed ecosystem?