I start the week with 105 syns. I count down, aiming for no fewer than 5 per day. If I go over, I still have my 5 per day til the end of the week. I don't go over too often, when I do, it's for a reason, like a big night out or something.
Like Ilovelife says, if I go over one night massively then start having no syns at all the rest of the week, it's too pressured. So in that situation, I aim for 5 per day and don't beat myself up if I gain because I had FUN gaining.
That way I find I don't just eat for no reason (apart from today when I'm on a 3pm-11pm shift and I've had 3 calls all day because lets face it, who cares about buying broadband on a sunday and the Snickers bar in the vending machine is just staring at me...)