It's not entirely clear what is causing the bug yet, but as of this writing (and for the past half hour or so), paid Android apps are not appearing on Google Play — either on the web store or on the Android client. As near as we can tell, it's mostly a listing problem: for example, the "Top Paid" section is gone, but paid apps that are editorially chosen by Google are still showing up. We also know that direct links to apps within the app store work — but only if you already have the link, as searches for paid apps don't list them in the results.

Update: We might not be entirely out of the woods just yet, but we are seeing some paid apps appear again on both the web front to Google Play and within the Android client — in both cases we were able to successfully purchase apps. There are still some gaps in the listings in both places, but it appears that Google is bringing everything back online.