I think thay make more noise than thrust... And they can make a lot of thrust!!!

The noise a pulse jet makes is mind boggling. Actually like putting a jack hammer on your head while being inside a large jet engine right besides a heavy metal concert.

Lot's of noise is the concept here

A nice explenation (and neat site) of how pulsejets work:
http://www.aardvark.co.nz/pjet/howtheywork.shtml