I like the idea of serials, and the Cube project I'm doing this summer will be my first real attempt at doing one. The interactive element intrigues me, especially in a community setting like fandom. I don't really think my existing series count as serials. All my installments have been far apart, and rarely did I even announce that there were forthcoming parts, so as not to raise expectations too high; I know quite well I don't usually work that fast, and I don't want to be a tease.

I think that for me the negatives would be a sense of guilt if I were running behind schedule getting new parts up, and a weighty feeling of obligation that might make the writing process less fun for me. On the other hand, I have that sense of obligation when I'm, say, writing for yuletide, and it actually seems to bring out my productivity, so I can't say for sure that counts as a negative.

As for the positives, there's the interactivity that I mentioned before, and also the ongoing encouragement that you bring up. It may also be that for some writers it makes them feel more committed to finishing the story.