Do you by any chance have any MP3 files used in the project? I've seen this eat up more than a fair share of CPU cycles at times.
Sorry for the late reply, but I found this to be worth replying.
When dealing with MP3s "straight", rather than converting them to AIF/WAV first, CPU useage is indeeed way higher than normal. On my Macbook, it's only useable when dealing with very little amounts of audio takes and effects. So, if that was the case, I would instantly convert the files to some non compressed audio data.
Really, pretty much the same as with video files. One may think that pure DV data would clog up the computer quite a bit, but it's in fact the compressed formats which do (due to the codec having to process all the time in the background).
- Sascha