I realized that the performance issues have something to do with the effect "Track Matte Key".
If I use this effect anywhere in my sequence (just anywhere. it doesn't even have to be where the playhead is placed. it only needs to be used only once in the whole arrangement), editing the Motion values in the program monitor becomes really slow.
When I remove the effect, it gets back to normal speed.
I am suffering from the same phenomenon since I updated just before christmas, I think.
I am hardly able to do scaling, rotating and translating in the program monitor itslef - whil motion has been highlighted in teh effect controls.
In the effect controls I can scale, rotate etc however.
Also I have noticed there is a yellow box with handles in teh program monitor. I remember it was white before.
I cannot figure out what to change in my preferences. What has happened?
Mac Pro OSX 10.7.5
16 GB 1066 MHz DD3
2 X NVIDIA GeForce GT 120 512 MB