One of the simplest ways of doing this, if you have Illustrator handy, is to turn on Illustrator's AICB support in preferences ("Clipboard Handling"), with "Preserve Paths" on. Then you can copy all the masks in a layer and paste them into a document in Illustrator.
If you're working with masks on Solids, the masks are fairly easy to copy. With Shape Layers, it is a little more tricky; you have to at least start with the path of the shape selected. It might be worth converting shape layer paths to masks on solids first. There's a script over at aescripts.com for that.