Depends on who 'you' are. I have one package I installed from the AUR and it's from a corporation that just repackages their builds. The problem is always who vets the packages. I trust the Arch team and I trust that one corporation. Also to use the AUR it's a different command, so I can't get surprised by an AUR package. It's not a pacman -Syu is going to pull in a new unknown to me AUR package.