yes, this is sorely missing. However, there is something in the works: akonadi and syncevolution.

As for now, I have stopped using kadressbook and kalendar on my ubuntu and use the N900 instead (for the same reason as stated above: the N900 is always there);
While I find kontacts and calendar on the N900 ok, the built in Nokia Todo i find rather substandard and not really usable.
Perhaps it changes in coming releases?