discovered the iPhone 3.0 beta firmware update currently prevents some users from downloading applications again.

Previously this was possible by sharing account details, but a message now reads: "You've already purchased this. You can redownload it for free on your computer, or tap Buy to buy it again."

Comments left on the iPhone Blog suggests the same message appears when you try and redownload free applications, which indicates this may be a glitch rather than a new feature to be introduced when iPhone 3.0 is released shortly.