TechCrunch dug up a bit more info on the media event Apple is reportedly holding later this month. According to the site's sources, the event will have less of a consumer focus (don't expect any new hardware), and it will be more about unveiling improvements to the iBooks platform to the publishing industry.
TechCrunch's sources haven't determined anything more exact than that, with the exception that this isn't expected to be a "major" event. I don't know about anyone else, but when I hear about "improvements to the iBooks platform" I immediately think, "iBooks for the Mac? I really hope you're talking about iBooks on the Mac, because next to the Kindle platform you're looking kind of silly without it."
No specific date for the event has been announced yet, but it's expected later this month.