a far classier version of "i like your style", originally used by pirates in the 17th century the expression refers to the forward sail on most ships. The course and speed of a ship is determined by the cut of the ships jib so saying that you like the cut of someones jib is a way of saying, i like the way you're heading.
Original 17th Century Pirate context:
A - I think we should mutiny, Yarr!
B - I like the cut of your jib (jim lad optional)!!!
21st Century context:
A - lets go for a beer and some readily available cannabis
B - alright, i like the cut of your jib