I used a poncho quite a bit at one point. They have their pros and cons. In serious rain you usually get wet. They aren't so great in wind. They tend to get in the way a lot.

I'm sure there are variations on the theme, and that some are better than others in certain conditions.

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I spoke with someone who does a lot of his riding and commuting in the rain (in the Northwest (Seattle)). He tried various systems, and what he ended up doing, and liked best, was using those thick, almost fleece-like cycling outfits (tights) made by Sugoi. They have a windbreaker fabric in front, and let the back breathe.

He said that the other systems just didn't work very well, and this one solved a lot of problems for him.