After some more thought about this, and some discussion with the people here, I've thought of another possibility.
Perhaps a column could be added to the variables table that is called:
billable_p
That way, mileage, and other variables could still be marked as something that can be billed to a customer. Is that suitably general that it would be of interest to everyone?
Then perhaps there could be a parameter per instance which indicates whether or not billale should default to checked or unchecked?
Lars and Peter: if I provided the patch for Postgres, would this be suitable for logger?
Any better ideas? I guess the easiest of all would be to have a separate variable: billable hours.
Perhaps that's the best solution of all.
