I did my top yesterday, and today when it rained, it left nasty streaks all down the sides of my car. Is that normal?

 

sounds like you didnt get the product off of the top-
(btw, common problem)
vinylex should be soaked onto a rag, then rubbed really well into the top. let it sit for a while and then i buff it down with a clean rag... and then buff it again exactly for the reason that you described.
if you buff it enough, the product will be in the material and not on it- and it wont run onto the car.
be sure to wash the car soon!