This is the understanding that most people have about power kite sports...and it is totally wrong. You can travel in nearly every direction if you
have the right wind, the right kite, and the right conditions. The kite is very similar to a sailboat, you tack with it the same way.
Moving on a board (or buggy) requires you to move across the wind not with the wind. If you travel in the same direction as the wind, you will
eventually catch up to the same speed as the wind - making the wind on the kite non-existant and your kite will fall to the ground like a rock. Ever
seen a young kid trying to launch a diamond kite while running in the same direction as the wind? Doesn't work very well at all.
Tacking across or 90 degrees to the wind will keep the same wind power on the kite at all times. As you have already guessed, you can travel in one
direction at 90 degrees, then turn around and head back to your starting point all the while your kite is powered up. With proper speed (and a good
quality kite) you can tack against the wind - also known as going or heading upwind. Different kites will produce different types of power while
heading upwind. Usually the higher aspect ratio kites will point into the wind further than lower aspect ratio kites (rider skills is usually the
main determining factor tho). By travelling upwind and tacking in different directions, you can go pretty much anywhere you desire - upwind,
downwind, across wind. The more skill you have, the easier it is to do.
Hope this helps.