My current implementation simply groups to-dos without a due date in a single entry at the top of the event feed. Due to limitations of the event view this is limited to 5 entries (rows) or 512 characters. All other to-dos without a due date are omitted and the number of the omitted to-dos is shown in the footer of the feed entry. I'm not entirely happy with that approach (it may be somewhat confusing that to-dos with a due date set are listed as separate entries).

I guess I'll implement the aggregate all to-dos mode suggested by you as well as the implementation I described above. Do you think that one entry which aggregates upto 5 to-dos is enough for day to day usage?