Tutorials/Water ladder

The Water Ladder was a structure to facilitate quick climbing in a strictly vertical manner. The accessible portion of this structure was a 1x1 shaft, but if created above ground would require 3x3 blocks of horizontal space. As of beta 1.6.6, water ladders have been demonstrated to work. They are harder to create and use, but still functional.

Aritelcs like this are an example of quick, helpful answers.

Ladders vs. Signs
It has been noted that this can be achieved by placing signs in front of the water outlets as well, but if the water is ever stopped, you can't climb signs back out.

Another reason to use ladders rather than signs is resource efficiency. It costs 7 sticks to make two ladders, or 1.75 planks for one, while a sign is comprised of 6.5 planks. Ladders also stack in your inventory, so you can carry more of them, or have room for other gear.

However, transport down is faster when using signs, one can simply fall down the shaft and then land on a pool at the bottom. When using ladders, you'll have to climb down.

Hidden Water Ladder
It was possible to make a hidden water ladder, but this was also affected by the Beta 1.6 bug-fix. To construct one, build your water shaft normally except put dirt or cobblestone where you would normally put the ladder. Then, move one space sideways, and dig a shaft upwards there. Face the corner where the water is and press up. Voila! Now hide your water source blocks and you're done. Using his method you can remove the usage of signs or ladders, but also makes it difficult (not impossible) to go downwards without damaging yourself, so this type is ideal for one-way up shafts. The other downside is that it only works when it is facing southwest (user facing the ladder).

Resources
There are a couple videos on YouTube featuring the speed of a water ladder and also the creation of one.