On the iPod Touch/iPhone since it is tied to your iTunes account, I am quite sure you can have your bought apps on multiple devices you own (can't test though iPod Touch was stolen).
However now I have the Motorola Droid, and am waiting for a tablet, and considering getting a Nook and rooting it to run my own apps.
Question is, if you buy an app on the marketplace, how is the security done:
- Is it tied to your Gmail account so you can share it between devices you own?
- Is it tied to the device? (Don't break/replace your phone!)
- As long as it's installed, you're OK? (If you uninstall, or wipe your device, it's gone).
I assume 3 is highly unlikely, though a possibility, so leaving it here as a potential answer to my question.