It’s gross. It is EXTREMELY popular in America. This explains why I have so many problems ordering a salad in the US. @Jeruba gave you the history above.
I can tolerate it in a cold pasta salad that I make, but I use very little of the stuff, much less than what the recipe calls for.
In the US we have ranch flavored potato chips also. Oh, and Doritos. Blech. It ruins some of the multipacks for me. My husband likes ranch, so he can have anything and everything with that flavor and leave me the plain chips.
Edit: people also serve ranch with Buffalo wings, which are spicy hot chicken wings. The wings are also usually served with celery sticks, some give the option of carrot sticks. People dip both the veggies and the spicy chicken in the ranch. Again, I have to say gross for me. The wings are delicious though.
I am very grateful that I hate the dressing/sauce.