The second most active topic is a sync system, see http://sourceforge.net/p/osmo-pim/feature-requests/search?q=labels:sync
. As I said, CalDAV would be a nice choice for calendar sync as it uses ics which osmo already supports. I've been able to import tasks from a CalDAV server (Owncloud) using the 'cadaver' command line tool and a bit of shell scripting. A plain text, file-system based storage for notes would be a great choice, users just have to use the tool of their choice to sync these files (Owncloud, Dropbox, Ubuntu One, Sparkleshare, Google Drive, Git, Spideroak, whatever...) between machines.
The third most active request seems to be tighter integration between components. Eg, being able to edit events from the calendar, linking to contacts/events from Notes.