[SyneRyder]

"There are also some unexpected restrictions on some titles, such as books that are viewable only on 1 or 2 of your devices..."

You can check this when purchasing on Amazon: the small print you're looking for in the Product Details section is "Simultaneous Device Usage: Unlimited". If you don't see that, it means your Kindle book is restricted (I believe to 5 devices simultaneously, though perhaps it varies from book to book.)

[fbags]

It varies from book to book. Some of them are only 1 or 2 devices. The annoyance is that I inevitably forget which books are device limited and end up unable to open them from work / while traveling / etc.