Yeah, my first thought on AO3 when it was announced was "... and we need another archive why?" But I really think they've done a great job with the overall design of the thing, especially considering what a huge range of different fandoms with very different needs that have to be accommodated! I didn't think I'd use it, and now I'm crossposting all my fic there.

ff.net ... yeah ... I know there are still a lot of people who read my fic there (I still get regular reviews) and that it's a one-stop-shopping zone for people who are new to fandom. But the formatting is such a hassle, and it's been so long since I uploaded a story that I've forgotten most of its weird, stupid little quirks, so I'll have to learn them all over again. :/