Update 2: And they're back. Crisis is averted!
Update: Google's now telling developers that it's aware of the issue. Help is on the way!
Everybody panic! Paid applications have disappeared from Google Play! Well, that's half true. They're still visible in the Android app, but trying to purchase just leads to an error. But the web portal (at least anything that's not on the front page) has been wiped of anything that costs anything.
It should go without saying (but we're about to say it anyway) that this certainly is a temporary thing. But we imagine there are a few developers of paid applications who are none too happy about this.
In the meantime, free apps are available for download, and books and music appear to be unaffected.
We've got an e-mail into Google to see what's going on.