Aren't we all forgetful from time to time. I know I am.
The problem with forgetting to fill in timesheets is that if you need to do it afterwards, it will take you much, much more time to do so. You'll need to backtrace your whole month (or even worse). I used to go through my calendar, installed latitude to keep track of where I was, at what time, I even had an app installed on my phone which filled a separate calendar with the phone calls I made so I could puzzle back together my timesheets.
Luckily that's a thing of the past. Now I track on the road thanks to our mobile app. If you (or your employees) are a bit like me you'll be glad to know that we introduced a new feature called 'Reminders'
Reminders let you specify your company holidays as well as days when you or your employees aren't working. Every user has a calendar which can be filled in with periods and type of absence (holiday, sick leave, etc...).