The following is a very quick summary. See the Sweeping Wind rune effects page for a more thorough description of rune effects, or any of the individual rune pages for numbers, screenshots, blue quotes, and much more.
During the beta, all the skills previously known as combos were simplified down so much that only three of them (Fists of Thunder, Deadly Reach, and Crippling Wave) still contain any semblance of combo functionality. These three skills now provide simply an additional effect on every third strike, while the others (Way of the Hundred Fists, Exploding Palm, and Sweeping Wind) now have a single function on every strike. Combos previously consisted of: the normal spell attack on the first strike; a stronger attack on the second; and on the third, an even stronger attack coupled with an additional effect.
Skill tiers were removed shortly before the beta started in September 2011, and Sweeping Wind became a level 17 skill. The skill system was once again overhauled for the Beta Patch 13 in February 2012, and Sweeping Wind was classified as a Techniques skill and moved to level 22.
For Beta Patch 14, it was moved to level 21. It was also significantly changed in function: previously, it was a Spirit Generating combo skill that struck a single target on every hit, and every third hit created the vortex effect.