I also letter count! I didn't even think about the fact that I did it until recently, I don't remember when it started, I'm now 17.
I wouldn't say I feel compelled to do it. I think I have quite an obsessive personality, without, luckily, the compulsive bit.
I also have a tendency to write words in 4 different styles in my head (joined up, flicky, straight & rounded). I repeat this until I can see the word written perfectly in each style.
It's so funny to think about this because I'm realising what I actually do with words which I've never thought about before! When I count the letters I group them in different ways until I find the most comfortable/fitting.
I feel a bit silly writing this, they're such pointless things to do.