The YouTube app for the iPhone is great and all, but when it comes to finding something specific, you've got to dig through all the garbage to find it. Plus, when you're looking for a movie trailer specifically, you'll really want to see the high quality ones that are available on the apple website. Trailers offers this exact type of service in two great packages, lite and paid.
The app is very straight forward. All you do with it is browse or search for a trailer of a movie that is out or is coming out sometime soon. Then you load the trailer up and watch it. The quality seems to be better then YouTube surprisingly, and you even connect to it faster than on YouTube. Plus, it's a subject specific search, so you won't be watching some 4 year olds Dark Knight trailer that his dad helped him make.
There's not a lot to this app, but as the iPhone is a multimedia device, having the ability to view the latest trailers in a high quality from anywhere is kind of nice. It really depends on how into movies you are. There are plenty of great movies out there that merit the use of the free app, but the paid app is really what you need to question.
Trailers is an app that you should definitely try out and see what you think. You'll spend plenty of time with the lite version watching through trailers for movies that you had no idea were even out. But only the most hardcore of movie fans will actually be purchasing this app, the rest will just be enjoying the trailer on YouTube.