The real biggest difference in my mind is the shift away from serial fic - stories that were intended to be read as WIPs and possibly continue on forever - to oneshots (which also contributes to the feeling of fic getting shorter, since the serial fics that would get emailed out sometimes seemed infinite in length).

There's a research paper in here somewhere! I wonder what would be a good way to quantify some of these trends so they could be tracked over time. Is it even possible? There'd have to be at least some element of interviewing or surveying in the methodology, at least to measure perception and changing habits.

I never subbed to mailing lists so I have no personal experience reading stories of that length posted in that fashion, and I've only read a couple on livejournal (e.g. Switch by ceres_libra in Star Trek: Reboot fandom), though I've seen a bunch (they pop up on fandom newletters, you can spot them by the "Part X/?" in the header); and it seems like a format that's still very popular on other communities, like ff.net. (ETA: I try to resist starting fics that look like they're being posted with no schedule or guarantee of completion since a) I've been burned in the past by abandoned stories, b) IMPATIENT READER IS IMPATIENT, and c) I switch fandoms so much that there's a good chance I won't still be interested in a story six months later when the author's finally done posting it. And if I am, I get to read it all in one shot, hooray!)

The possibility for comparisons across media is also intriguing, as "serial fic - stories that were intended to be read as WIPs and possibly continue on forever" sounds like nothing so much as the definition of a soap opera.