I think that this would be useful for service companies that bill for time. Project management would also be good.
I agree! I have struggled to adapt xTuple for Service based organisations. You can create service based products but the delivery of services is overly complicated as xTuple is set up for the delivery of physical products.
However the entry of time can be a very complex thing and would require quite a bit of effort to add to xTuple.
I am currently considering the use of a third-party web-based time entry system and building integration of time entered in that system into the creation of xTuple Sales Orders. Something similar to the osCommerce integration.