Saw this interesting tid bit from Film and Video magazine:

(http://www.studiodaily.com/filmandvideo/currentissue/features/5357.html)

-But support for editing HDV in its native format is gaining currency in the NLE world, especially among vendors who say any quality hit during image processing is minor. "You will never do repeated re-encodes in Final Cut Pro," says Paul Saccone, Apple’s product manager for Final Cut Studio. "If you take an HDV stream, whether you’re doing color-correction or a 16-layer composite, we decompress all that video into a 4:4:4 color space, do our composites, and then do one single re-encode back down to the HDV format. So you’re only, ever, incurring one generation of re-encoding."-

Interesting stuff, and can explain a bit about why hdv rendering seems to be so slow... But good to know you will only lose one generation no matter how much post work you do on your footage.

This is not limited to HDV. You won't have more than 1 re-encode in Final Cut Pro, no matter how many layers, tracks and effects you use. Final Cut Pro decompresses the source material necessary to create the final canvas image and applies all filters and blending effects on the decompressed source material before compressing it back to the sequence codec.

The downside of this is the fact that whenever you change a single effect all other effects will have to be rendered again. If you're using slow effects like nattress film effects combined with 3-way color correction, changing something in the color corrector will necesitate the film effects render to be redone.

Another downside is that moving some footage in a track above another track will cause a render of the place where the footage was and the place where the footage has landed, if the upper track has less that 100% opacity or uses a video blend mode different from normal. This wouldn't be necessary if Final Cut Pro would render per track, but as written above, it doesn't.

You have to think about Final Cut Pro rendering as a vertical type of render (rendering each frame of the timeline at once across all tracks), instead of a horizontal (per track) render.