So much of this is cultural and I don't think any organisation gets it 100% right all of the time and we're no exception.
That said, things we have done:
For contractors, agencies will only pay them if the individual has submitted a copy of their timesheet to the agency each week (we have a report that gives them a print out). That keeps contractor timesheet compliance pretty high :grin:
Put a portlet on the overview page for each user that tells them if they have outstanding timesheets (obviously they can still ignore it but it's better than nothing....horses to water and all that!)
Done a similar portlet for managers/programme office to allow them to look across their areas.
Periodically issue stats on compliance by area.
As Clarity timesheets ultimately feed our internal recharge process that also gives a bit of impetus to getting the data in.
Owen