Gordon Weakliem calls me out on the GUID usage here:

RSS 2.0, RSS 1.0, and Atom all provide a way to handle post identity: the <guid> element, the rdf:about attribute, and the <atom:id> elements, respectively. Unfortunately, not everyone provides this metadata, or does it incorrectly: for instance, CNN doesn't give you GUIDs , the Cincom weblogs just use big integers (these look like they might be dates, but I'm not sure), and PHP.NET is re-using the rdf:about attribute on different posts. The problems, from last to first: if you identify posts by GUID, re-using a GUID amounts to modifying a post, though that doesn't seem to be the intent in this case. Using big integers is poor practice, because an integer isn't a GUID. Recall that the GU part stands for globally unique : if you use integers as GUIDs, you're just hoping that there won't be a collision, especially if your protocol is to increment a counter with each new post.

Yeah, I know I should be using the full post link for the ID instead of the number. In my case, the ID is only unique within a given blog, not necessarily across all blogs on the site. The number is a timestamp, so it's a pretty sure bet that it'll be unique within a given blog. If I had it to do over again, I'd do it differently. I just don't know that I want to flash every subscriber with faux new posts. I probably should at some point.