I recently started using the Amazon App store, and noticed that it copies the apps I already purchased or downloaded to other Android devices if I sign in using the same account. Is there any specified limit on the number of devices that this is supported on? If I have 10 Android devices can I buy an app once and install it on all of them?
Yes, you can install all the apps you buy from the Amazon appstore on any device which is linked to that Amazon account. It operates just like paid apps in the Android Market which are available to all the devices associated with that particular Google Account.
I have 3 Android devices and all they are all linked to the same Amazon account and the same Google account and when I purchase an app through the Market or the Appstore I have it on all three devices.
The max is 25. It'll tell you that your username or password is wrong if you try to auth any more. Though it's pretty easy de-authing them from the amazon website
Found a source: http://forum.xda-developers.com/archive/index.php/t-1315474.html
Applications purchased are tied to your Amazon account. You can also tie multiple devices to your Amazon account. However, every device must have the Amazon Appstore app installed on it and must be logged in to access the apps installed via the Amazon Appstore, which would give anyone with any of these devices the ability to purchase additional apps using your Amazon account and it's payment information. So, as the Amazon help describes it, it does look like it's possible. However, it also looks like a really bad idea unless you absolutely trust everyone who has each of these 10 devices.