I'm aware that you can sync an iPad with up to 3 different computers, but if you have multiple iPad devices with the same iTunes account, how many devices can you sync an app to?
As far as I know, there isn't a limit. As long as the account is associated with the device, then any apps from that account can be put onto that device. If you own more than one device, you don't have to purchase the app again. You could own one hundred iOS devices and pay for just one app.