Most of what turns up when you search on the topic of "microcontent" is e-mail related. Jakob Nielsen wrote an oft-cited Alertbox column in 1998 on microcontent, which is a list of guidelines rather than the results of research. WebWord did some limited research on e-mail as microcontent to verify Nielsen's assertions.
Corante has a site on microcontent, which is subtitled "the online magazine for weblogs, webzines, and personal publishing"--but which focuses primarily on blogs.
Preliminary searches of academic databases (excluding ACM, whose "portal" doesn't seem to work properly) show no published research on the topic of "microcontent," and only informational pieces on blogs (as opposed to research), so there seems to be a real opportunity here.