When XMPP support in Google App Engine was announced, it occurred to me that it would be pretty easy to use it to do a PubSubHubbub-to-XMPP bridge. Other things came up, but I was reminded again of the possibility when a "Oh, you didn't you see my Reader share?" conversation happened in a Partychat room. A bit of searching turned up someone else with the same idea, except it wasn't quite as user-friendly as it could be (i.e. as user friendly as a quasi-command-line interface, which isn't saying much).
After a bit of weekend hacking I've created PuSH Bot, which lets you subscribe to any PubSubHubbub-enabled feed and get notified of updates via XMPP (e.g. to your Google Talk account). It has some niceties like use of feed auto-discovery so you can just specify web page URLs, OPML import for bulk subscribing and throttling of updates. The homepage lets you know how to get started.
The code is available, though there shouldn't be anything too special about it. Feed parsing is done via ROME (as is OPML parsing, though that needed some patching to get working). Feed auto-discovery is handled by Google AJAX Feed API because life is too short for HTML parsing.
Update on March 13, 2015: The App Engine App was migrated to the High Replication Datastore, which necessitated changing its app ID to push-bot-hrd. The URL should still redirect, but chat messages may not, so if you have subscriptions you may need to re-subscribe.