[ATDrake]

1) Amazon won't delete your books; not after the 1984 fiasco. Though if you're concerned about the possibility, you should keep backup files of them and look into DRM-removal (still legal in Canada, despite the proposed Bill C-32 which seeks to restrict our fair usage rights to an absurd degree, and which you may perhaps want to write your MP to oppose) if applicable.

If your book said on its product page "Simultaneous Device Usage: Unlimited", that's generally a code for DRM-free; no removal is required and you can simply copy it to your other devices without compatiblity issues.

2) Amazon do allow for people moving and having holiday residences, which is why you can enter more than one associated address for your Kindle and switch between them at need. The trick is not to do it too often, or unrealistically (New Zealand to US thrice in 2 weeks, say).

If they catch you, apparently your account may be blocked until you supply them with official proof-of-residence documentation (this has happened to at least one person here on MR).

3) As for how Kindles get swapped around, on the Manage Your Kindle page on your Amazon website account, you can see the info for your Kindle registrations, both physical and app.

For each device, there's an option to deregister, which is how owners remove their Kindles from their accounts before reselling them, and incidentally freeing up one of the normally allowed 6 device licenses for DRM copy-protected books. You can add a Kindle registration in the same way, by putting in the serial number for an unregistered Kindle, or you can do it directly from the device itself, by going into the Settings and entering your Amazon account/password.

4) You can only have your Kindle registered to one account at a time, but you are freely able to de-register and re-register them back and forth as you like, which is how families and sometimes friends will "share" books by temporarily registering the Kindle they want to read upon to the account which has the desired books for just long enough to download the necessary file.

It's very useful in case you want to keep your reading/purchases separate from, say, your kid's (they would normally have access to everything in your archives and the 1-click online buying capability unless their own Kindle was deregistered shortly afterward or you maintained a separate account).

People are sometimes worried about age-inappropriate material and this gives them a modicum of control if they wish to vet their children's reading material (the Kindle has no built-in parental controls, in case you were wondering). Also useful for multi-Kindle households where people have very different reading tastes/spending habits and don't want arguments about going over budget on a joint account or divvying up the expenditures.