I used some Kevlar to strategically reinforce the underside deck of my expedition single. In an experimental, because I could sort of fashion.

Plusses

Now, this is all folk lore, but I understand that Kevlar is about 40 x stronger than regular glass cloth. Theoretically you could get great weight savings by using much lighter kevlar cloth than you would if you were to use glass cloth and still have the same (if not more strength).

However, strength in this case is a relative thing. Kevlar is very abrasion resistant but it is more flexible than glass cloth, so you would probably want to reinforce the kevlar with something to make it stiffer. For example Carbon (which tends to be so stiff that it is brittle on its own) = carbon reinforced kevlar.

Minuses

Kevlar is expensive
Kevlar is a devil to cut - regular scissors won't work
Kevlar is very hard to wet out (sort of like a water proof sponge - if there ever was such a thing)
Once Kevlar has been epoxied, it is hard to repair if it gets damaged - sanding just makes the weave fuzz up.

Basically I never used kevlar ever again, resorting to layered carbon with glass either side to areas where I wanted stiffness and shape holding (like hatches and immediately around them).

All just my humble opinion and may or may not have helped.

Cheers Pete