There are times when I purposely don't use my blinker. If I am in traffic, I make a point of not using it. As soon as I flip my blinker on, the car in the next lane purposely speeds up a bit so that there won't be room for me to get in. It happens almost every time. So, by not using the blinker, I have that element of surprise and can get into the next lane. Of course there are times where the car in the next lane will try to speed up anyway, but I'm generally quick enough to get in there. I really don't understand the mindset of these drivers that purposely try to cut you off and prevent you from changing lanes, whether your blinker is on or not. They obviously have issues and hogging up their lane gives them some sort of feeling of superiority. Me, I don't worry about silly things like teaching another driver a lesson if they don't use their blinker. I also don't make their lives harder by purposely speeding up so they can't get in my lane when they do use a blinker. I have better things to do with my life. I guess these other drivers feel special by being the "perfect driver police".
In most other circumstances I do use my blinker.