As a contact, it would help with thrips that are out in the open. But thrips do the most damage while inside buds, where a contact would be useless. And since thrips eggs are laid inside plant tissue, it won't help there, either.
Here is a very informative link about horticultural oil, how to use it, when to use it, and what it does and does not do.
http://gardening.about.com/od/...
