UPDATE: Per comments below, this only seems to be effecting some users and only on 3.0 Beta firmware. We've also added a poll in the forum so we can see what everyone thinks. Beta behavior changes.
Looks like Apple's begun charging full price if you try to download an app you've already bought over the iPhone. This did not used to be the case -- previously you'd be given a dialog stating you'd already bought it and you could go ahead and re-download it for free. Now the dialog says you can still re-download it for free on your computer (via iTunes), but if you want to download it again directly to your iPhone, you've got to buy it again.
What's going on here? Not bandwidth control, since free apps and updates to paid apps are still free. Not device restriction, because you can still re-download for free via iTunes (though it's not as convenient, of course).
We're guessing that with the on-device account management coming to iPhone 3.0 -- where you can log in and out of multiple iTunes accounts right on your iPhone -- Apple is putting this in place to prevent the sharing of purchases between accounts. (Otherwise you could just log into 100 other iPhones with your account and give them all your paid apps right over the air).
We can understand the concern, but we'll miss the functionality. For example, I personally used the re-download ability all the time for app management. E.g I bought a FedEx tracking app that I delete when I'm not expecting anything and re-download when I am. Now I can't do that any time I want any more -- only any time I'm at my computer. I'd much rather keep that and ditch multiple accounts.
What do you think, is multiple on-device accounts worth the loss of free on-device paid app re-downloads?
[Thanks Jordan for the tip, iPhoneDocked for added confirmation]