i think its unlimited since the apps are whats the word licensed? to your account and you can do what you want since you purchased it only limited to the amount of idevices you can buy
Well, I read somewhere (**********) that Apple plans to start charging you for downloading apps after the first iPhone. Can you imagine how horrible that would be? http://www.**********.com/news/apple-to-begin-re-charging-for-downloads/
Think I have 6 or 7 idevices to my account. Music is five limit though. Although only two are really active. Usually what I do is get someone to buy an ipod touch for instance say brother-in-law. I load up all my games and say test em out for a couple months and take note what you like. Then when they're ready to starting buy their own games/apps they lose all the ones I put on there. Anyway good way to give them a taste of everything.