It looks like Apple may be on to the "account sharing" loophole with the App Store, because iPhone 3.0 firmware is going to make you go to iTunes to re-download apps you've already bought. Here's how the loophole works:
Currently, you're able to hook your friends up with free apps by logging their phone into your iTunes account. Then, when they go to buy an app you already own, iTunes lets them download it again for free. No more!
It'd be a mild inconvenience to have to sync your phone up with your computer to redownload apps you've already bought, but it's a move by Apple that's pretty understandable. Way to ruin it for the rest of us, unscrupulous loophole-exploiters! [The iPhone Blog via ZDNet]