I've started cycling to work and am trying my hardest to monitor my calories.
I've resolved myself to monitor my calories even if they are way over, non of that "I'll start again next week/tomorrow." This was a suggestion of a friend and I think it is quite right, apart from anything else you need to just think of it as data and feedback and not get too emotional about it. Or rather feel good if you do manage to hit your goal but not bad if you you don't. Instead of feeling bad look at what went wrong and try and do something about it.
Furthermore often when you miss your target you actually find that you only took yourself to a sustaining level of calorie consumption or a lower weight loss rate, you don't know if you don't enter it.
Finally don't let precision stop you, it does not matter if you get the calorie count exactly right, estimate if you have to, it is better than not bothering.