I believe if your first jump is in a certain direction you will blink in that direction as well.
For example, your first jump is to the north, and you turn east mid jump, you tap the jump button to blink. You still end up blinking to the north I think. Same can apply even if you jump backwards I believe. You blink backwards.
Blink is purely on a horizontal plane only, no vertical blinking.
Blink distance appears to be about 3 or 4 meters too.
So blinking is good for getting away, and moving around horizontally, but you sacrifice the vertical versatility completely. So gotta choose, vertical or horizontal versatility.
Using blink in conjunction with blink strike could be very useful in pvp, especially if you are behind someone a decent distance and they are sprinting. Blink to make up 3/4 meters, and blink strike right away to make up another 3/4 meters. If you have the ability that increases damage significantly when blink striking from behind then it becomes a 1 hit melee kill instead of the two needed for normal melee. Plus you don't give your position away because you had to shoot the guy to get the kill.