I've had both good and bad experiences.
It's all in the skill of the practitioner/beautician. If the lashes aren't set properly, they can kink or cross over and if the bottom lashes aren't protected properly, they can turn funny too. They should really wash off the 'perming' solution with water in a bowl. Not just dab at it with cotton buds.
Avoid any beauticians who are available straight away when you try to book. Always go with somebody who is booked up months in advance.