There are basically two scenarios for using iShowU with Final Cut Pro (FCP). You would either want to mix iShowU recordings with existing footage either shot or acquired, or you need to create high quality recordings that will need further editing and then finally export to another format (DVD, export to web, etc.)
With either case, the most important thing is matching the iShowU settings to the FCP project settings. FCP will complain (in a number of ways) if these settings don't match. The important attributes are:
If any of these settings in the video differ from the FCP project, FCP will likely complain with General Error, error messages about the video not being optimized. In addition, if the settings aren't right then you won't be able to preview your edits in place without first rendering.
In this example, some footage has been shot with a mini-DV camera and then captured into FCP. Your sequence setting should then typically look like this. The arrows point to the key settings which you will match in iShowU. To find out your Sequence Settings in FCP, press (Apple+0)

Your iShowU recording setting should match these settings.

Notes on Video Formats
It's common these days to shoot or acquire footage in a Widescreen format (16x9). if that is the case, in your FCP sequence settings, you would have the "Anamorphic 16x9" Check box "On"
In iShowU you would then make an adjustment to your "Capture Size" to accommodate for the wider aspect ratio. In this case, your capture size would be 852x480.
First decide the final destination of your video recordings (web, DVD, TV etc.) and plan your recording settings according to your final delivery. The key here again is to match your FCP settings to that of your iShowU recording settings. A few things to note:
Aspect Ratio and Field Dominance. Because your recording is straight from your computer, you will be working with Square Pixels (or a ratio of 1:1). Also, when you capture on your computer, there is no interlacing (progressive scan). For this example, I would want to record a High Definition video for edit into FCP and then export to web video. Your sequence settings would look something like this.

Compression. You would ideally work with video that will be high quality and easy to edit with. Choose either "Apple Intermediate" or "Apple Animation
