I've just downloaded Cheeseholes
tile veg demonstration file (nice one).
Play back is what you might expect with a generated media heavy project that includes gausian blur - ie a bit choppy. Fair enough, not a problem.
Then I dragged a dv clip onto the timeline
after the end of the generated section and found that play back preview frame rate was still reallyl slow. I started to mute the various tracks that held media. It was when I muted track 5 of that project, which uses the gaussian blur filter that suddenly the playback rate returned to full real-time.
So, is this a bug? Track five is set to 'multiply' (mask) so I think this partly explains the behaviour, but surely it shouldn't effect video on the new track further down the timeline?