It would be nice if other events than conversation messages could also be logged.
Each can be optional to avoid a large log. Some of these events may be protocol specific:

- Change of public alias/nickname

- Change of avatar, i.e. store each previous avatar and when it was introduced
Reoccuring avatars use one same file, but all datetime events are kept

- Change of general status (including login/logout) as well as any custom status messages

- File transfers (from, to, filename, size, starttime, endtime, possibly hash digest)

- Request to add contact on list, both incoming and outgoing, plus its response later

- You were removed/unsubscribed from someone's contact list

- Incoming IRC requests like PING

- Local ignoring/unignoring actions towards a contact