In fact, I think that would be fairly elegant. That way each time a person gets assigned a task, be it in the context of a project or in an operational context he's instantly able to book time on that particular task. By making the UI intiutive, it doesn't matter to the user whether they book on projects or on tasks. Whether or not you use that kind of detailed info is another case, but then at least it's there.
On a related topic: I was thinking a bit further about my own remark about posting something in alt.projectmgm etc. Could we perhaps setup a survey to 'poll' for what people think of as 'the ideal set of tools'? Not that we should build that - just to get ideas.
Or, Nick, have you already encountered such a thing?