Focus Plug In
 

Is there a plug in for FCP that allows you to mask areas of the frame and blur them to give an out of focus or soft focus look?

If you have FCP6 you already have a defocus filter built-in, but it does not have any auto-masking feature.

You can mask any part of your image and use any filter for the masked area using the various garbage masks also built-in to FCP or, you can create a hybrid mask by using layers of the same clip and opacities. Either method will get tricky if the masked area moves around in any way.

Normally this type of thing would be best accomplished by After Effects or Motion but it can be done in FCP - with a lot of work and a clear understanding of how to mask and use layers; unfortunately there's not enough room in a forum thread to teach such a task however there are a multitude of DIY videos on the subject from various sources such as Lynda, Digital Juice and a few others. I'd reference those videos first before attempting the task.

you're welcome to use my free FxScript plug in to do it
http://web.mac.com/andymees

you'll want the one called Andy's Region Blur

have fun
Andy