I must confess that I never saw much use (or need) for Atom here, but being fundamentally fed up with the way Technorati mis-parsed my posts (it couldn't figure out post boundaries), I finally descended into the grim dungeons of the PhpWiki RssWriter code, subclassed the hell out of it, and did the appropriate tweaking in RecentChanges.
So my Wiki now has a spanking new Atom feed (the URL for which is here), and I will be experimenting with it for the next couple of days. If it works, then it will become the new default everywhere (including individual RSS feeds for each Wiki node). And, of course, it uses my feed caching technique, so you should only get new items on each poll.
If instead of whining you can tell me exactly what is wrong, I'll gladly fix it. Constructive criticism is always welcome.