This has just started happening, as of around the 7th of November (I think). There's data being piped everywhere, so it's a little hard to track, but I think the problem is with FeedDigest.
Basically, I'm getting items' HTML show up rather than the item itself. Example: http://exmosis.net/ - angled brackets are being converted into character entities somewhere along the line. (Previously, the HTML would be parsed OK and everything would look nice.)
I'm using FD to aggregate the various blogs, and judging by my FD RSS feed, it's happening there somewhere.
Can't think of anything I've done to change the behaviour. Any thoughts?